Method and apparatus for inspecting samples, and method for manufacturing devices using method and apparatus for inspecting samples

ABSTRACT

A method for alignment of a chip in a substrate surface inspection is provided, in which a surface of a substrate including a chip formed therein is inspected by using a beam. The method is characterized in comprising: a step of placing the substrate so that the chip is positioned within a field of view subject to the inspection; a step of measuring a magnification for the detection when the chip is positioned within the field of view subject to the inspection; a step of calculating a size of position error of the chip based on the measured magnification for the detection; and a step of compensating for the position of the chip based on the calculated position error.

BACKGROUND OF THE INVENTION

The present invention relates generally to an aligning method of a chip,an apparatus and method for inspecting samples using the same aligningmethod, and a method for manufacturing devices using the same apparatusand method, and specifically to: an aligning method for performing adefect inspection of a device pattern having a pattern of size equal toor less than 0.1 μm formed on a surface of a sample, such as a stencilmask, a wafer and the like, with a high precision, a high reliabilityand a high resolution, and also with a high throughput; an apparatus andmethod for inspecting samples using the same aligning method; and amethod for manufacturing devices, which includes a step of inspectingsamples by using the same apparatus and method for inspecting samples.

An apparatus for inspecting a sample for defects is typically operatedin a manner in which an electron beam is irradiated onto a sample to beinspected, such as a wafer, to thereby generate electrons containingdata related to a device pattern formed on a sample surface to beinspected; the generated electrons are then used to form an image of thedata representing the device pattern; and thus obtained image isinspected in accordance with a predetermined inspection program. Toimprove the reliability of the result of the inspection, it is requiredthat data having a high precision should be obtained from the devicepattern on the sample surface through the irradiation of electrons. Onemeans to address this is represented by the registration of a stage inthe X-axis and the Y-axis directions, which carries the sample thereonand moves in the X-axis direction and in the Y-axis direction orthogonalto said X-axis direction, and by a focus adjustment in the Z-axisdirection parallel with the axial direction of a secondary opticalsystem.

In the practice according to the prior art method, taking as an examplea case where images for two regions corresponding to each other aregenerated from the wafer surface to be inspected and thus obtained twoimages, or one of the image and another corresponding image areinspected for any defects, such a method has been typically employed, inwhich for said one image, a plurality of images is generated each takenby shifting a position by +1 pixel, +2 pixels, −1 pixel, −2 pixels,respectively, along the X-axis direction and the Y-axis direction, and atotal of 25 thus obtained images consisting of those 24 shifted imagesplus 1 not-shifted image are compared with the other images, wherein adefect inspection apparatus using a single electron beam has been putinto practical use for forming those images.

Further, an inspection system using a multi-beam to perform a defectinspection of the samples has been also suggested in order to improvethe throughput (see, for example, Specification of U.S. Pat. No.5,892,224 and B. Lischke, Japanese Journal of Applied Physics, Vol. 28,No. 10, p 2058). There is another known method, in which a rectangularbeam is irradiated onto a sample, and an electron beam emanated from theirradiated point is magnified by a projection optical system fordetection (see, for example, Japanese Patent Laid-open Publication No.Hei7-24939).

Those systems that carry out the defect inspection using a plurality ofelectron beams with which a plurality of regions can be scanned at once,may be considered to theoretically improve the throughput in proportionto the number of electron beams.

The above-described inspection apparatuses for a pattern defectaccording to the prior art, however, have been associated with a problemthat it could be difficult to perform an accurate inspection, which maypossibly be arise for the following reasons:

(1) Although a stage is installed for carrying a sample thereon andmoving therewith in the X-axis direction and in the Y-axis directionorthogonal to the X-axis direction, there might be a case where adistortion is induced in a stage guide serving for guiding the stage, oranother case where the stage guides in the X-axis and the Y-axisdirections are not crossing precisely at a right angle with respect toeach other, which would prevent the stage from moving along an idealtrack;

(2) Upon placing the sample on the stage, there might be a case where anX-Y coordinate of the sample is not aligned with an X-Y coordinate ofthe stage, and so an error would be generated in a rotational direction;

(3) There might be a case where an error is introduced in a laserinterferometer for detecting a position of the sample;

(4) There might be a case where, in some samples, the die could beformed in a position offset from its designed position in thelithography process;

(5) There might be a case where a variation in moving speed is inducedduring a continuous movement of the stage; and

(6) There might be a case where a charge-up is induced in the sample bythe irradiation of the electron beam and a resultantly obtained imagecontains a distortion generated therefrom.

If the errors described above are not somehow compensated for, theobtained image could be offset from its theoretical position by ±2 ormore pixels, for example. If there is a possibility that said offsetoccurs to an extent defined by each ±3 pixels in the X-axis and theY-axis directions, then in order to ensure accurate defect inspection,the number of images to be generated for the comparison should be asmuch as 7×7=49. Consequently, with the above systems there could be adisadvantageous situation that the number of memories and comparatorcircuits required for the inspection must be increased, which in turnleads to a problem that the rate of the defect inspection could nolonger keep up with that of the image taking, and accordingly the defectinspection could not be performed with high throughput.

In addition, in the defect inspection of the samples according to theprior art, as described above, simply the registration in the X-Ydirections is typically practiced prior to two-dimensional image takingfor subsequent pattern inspection, but an uneven surface of the samplehas not been taken into consideration. From this reason also, it ispossible that highly accurate image signals will not be obtained.

For example, a defect inspection apparatus using a projection opticalsystem, which is known as an apparatus for obtaining a two-dimensionalimage for inspecting a sample or the like for any defects in the sample,has been associated with a problem that a magnification of a secondaryelectron image varies significantly over time or in response to anychanges in the environment, such as a temperature change. Further, sucha projection optical system has another problem that if the surface ofthe sample is uneven, a resolution of the two-dimensional imagedeteriorates because of a shallow focal depth of the system.

Yet further, those defect inspection apparatuses according to the priorart have been associated with a problem that an accurate defectinspection can not be carried out due to a frequent variation in themagnification of the image projection optical system, and in addition,no special attention has been paid to a need for an accurate measuringof a scanning sensibility of a multi-beam optical system, and also noreference specifically disclosing this matter has been found.

Still further, for the SEM using a single beam, since it comprises asingle beam and a single detector, and accordingly the density of thesignal fully represents data on the sample, therefore the defectdetection can be performed by simply carrying out the pattern matching,but for the case of using multi beams, since the multi beams contain thevariation in its beam current value by some percentage among respectivebeams and also has a difference in the detecting sensibility amongrespective beams. Therefore, the density of the signal is notnecessarily representing the data on the sample exclusively. Besides,the defect detection method using the projection optical system has aproblem that the density of the signal could be different even for thesame pattern section in a sample depending on whether it is located inthe marginal area of the field of view or in the area adjacent to anoptical axis, and this may lead to a frequent detection of false-defectduring the defect detecting operation.

SUMMARY OF THE INVENTION

The present invention has been made in the light of the above problems,and a first object thereof is to provide an aligning method forperforming an aligning operation after measuring of a magnification whena rectangular beam is used in a sample inspection apparatus ofimage-projection type.

A second object of the present invention is to provide an aligningmethod for performing an aligning operation after measuring of ascanning sensibility when a multi-beam is used in a sample inspectionapparatus of multi-beam type.

A third object of the present invention is to provide a defectinspection method for performing a defect inspection by using such analigning method as described above.

A fourth object of the present invention is to provide a method andapparatus for inspecting a pattern, which allows a defect inspection tobe performed with high accuracy even in a case where a manufacturingerror of the defect inspection apparatus (a distortion in a stage guide,an orthogonal error in the stage guide) and an error relating to apositioning of the stage during its traveling motion are in aproblematic level and/or a die on a sample has not been formed on anideal coordinate in conformity with the theoretical value, as well as inthe case where the moving speed of the sample is not constant.

A fifth object of the present invention is to provide an inspectionmethod and apparatus which allows a two dimensional image to be obtainedwith high accuracy, high reliability and high resolution, even if themagnification in a projection optical system varies and/or even if asample surface is uneven.

A sixth object of the present invention is to provide a defectinspection method that can prevent any false-defects from being producedin a multi-beam or a projection optical system.

A seventh object of the present invention is to provide a devicemanufacturing method, in which a high throughput can be expected bycarrying out the defect inspection using the above-described inspectionmethod and apparatus.

According to an invention as claimed in claim 1, a method is providedfor aligning a chip in a substrate surface inspection, in which asurface of a substrate including a chip formed therein is inspected byusing a beam, the method comprising steps of:

placing the substrate so that the chip is positioned within a field ofview subject to the inspection;

measuring a magnification for the detection when the chip is positionedwithin the field of view subject to the inspection;

calculating a distance of misalignment of the chip based on the measuredmagnification for the detection; and

compensating for the position of the chip based on the calculateddistance.

In the method for aligning a chip in accordance with claim 1, the stepof measuring a magnification for the detection when the chip ispositioned within the field of view subject to the inspection mayinclude steps of:

obtaining an image of a structure having a previously known actual size;

determining the number of pixels in the image of the structure; and

measuring the magnification for the detection from the actual size ofthe structure and the number of pixels. Further, in the method foraligning a chip in accordance with claim 1, the step of measuring themagnification for the detection may include a step of obtaining at onceany two of an X-coordinate, a Y-coordinate and a Z-coordinate indicatingthe position of the substrate.

According to an invention as claimed in claim 4, an inspection method ofa substrate surface is provided, in which a surface of a substrateincluding a chip formed therein is inspected by using a beam, the methodcomprising steps of:

placing the substrate so that the chip is positioned within a field ofview subject to the inspection;

measuring a magnification for the detection when the chip is positionedwithin the field of view subject to the inspection;

calculating a distance of misalignment of the chip based on the measuredmagnification for the detection;

compensating for the position of the chip based on the calculateddistance;

irradiating the beam toward the surface of the substrate in which theposition of the chip has been compensated for;

detecting a back-scattered beam containing the data obtained on thesurface of the substrate;

obtaining an image of the surface of the substrate from the detectedback-scattered beam; and

performing an inspection of the substrate by using the obtained image.

In the inspection method of a substrate surface in accordance with claim4, the step of measuring a magnification when the chip is positionedwithin the field of view subject to the inspection may include steps of:

obtaining an image of a structure having a previously known actual size;

determining the number of pixels in the image of the structure; and

measuring the magnification for the image from the actual size of thestructure and the number of pixels.

Further, in the inspection method of a substrate surface in accordancewith claim 4, the step of measuring the magnification of the image mayinclude a step of obtaining at once any two of an X-coordinate, aY-coordinate and a Z-coordinate indicating the position of thesubstrate.

According to an invention as claimed in claim 7, a method is providedfor aligning a chip in a sample surface inspection, in which a surfaceof a sample including a chip formed therein is inspected, the methodcomprising steps of:

-   -   (a) moving a stage so that a dicing line in a corner of a sample        or a characteristic pattern on the sample comes into a field of        view of an optical system in a defect inspection apparatus;    -   (b) irradiating a beam onto the characteristic pattern on the        sample, detecting back-scattered electrons or secondary        electrons from the sample by a detector and obtaining a        two-dimensional image;    -   (c) storing a coordinate of the stage (Xc, Yc) when the        two-dimensional image is obtained in the step (b);    -   (d) moving the stage and thus the characteristic pattern by a        certain distance within the field of view;    -   (e) performing the same operation as the step (b) so as to        obtain the two-dimensional image of the characteristic pattern        in the moved position;    -   (f) storing a coordinate of the stage (Xf, Yf) when the image is        obtained in the step (e);    -   (g) applying a pattern matching between a portion of the image        obtained in the step (b) and the image obtained in the step (e)        to calculate a displacement between the two images in the X- or        the Y-directions (ΔX pixel, ΔY pixel);    -   (h) calculating a difference between the coordinate (Xc, Yc)        stored in the step (d) and the coordinate (Xf, Yf) stored in the        step (g), defined by (Xf−Xc) or (Yf−Yc);    -   (i) calculating a size per pixel, (Xf−Xc)/ΔX or (Yf−Yc)/ΔY, or a        magnification of a projection optical system;    -   (j) storing the size per pixel or the magnification of the        projection optical system, which has been calculated in the step        (i), into a memory; and    -   (k) calculating a moving distance of the stage by using the size        per pixel so as to perform the alignment operation.

In the method in accordance with claim 7, the beam used in the step (b)may define a shape having a longitudinal axis in one axial direction andthe beam may be controlled by a deflector so as to scan the field ofview along the other axial direction, while, in synchronization with thescanning, an optical parameter of a secondary optical system may bechanged.

According to an invention as claimed in claim 9, a method for inspectinga substrate surface is provided, in which a surface of a substratehaving a chip formed therein is inspected by using a beam, the methodcomprising steps of:

-   -   (a) placing the substrate on a stage;    -   (b) moving the stage so that a dicing line in a corner of a        sample or a characteristic pattern on the sample comes into a        field of view of an optical system in a defect inspection        apparatus;    -   (c) irradiating a beam onto the characteristic pattern on the        sample, detecting back-scattered electrons or secondary        electrons from the sample by a detector and obtaining a        two-dimensional image;    -   (d) storing a coordinate of the stage (Xc, Yc) when the        two-dimensional image is obtained in the step (c);    -   (e) moving the stage by a certain distance and thus moving the        characteristic pattern, within the field of view;    -   (f) performing the same operation as the step (c) so as to        obtain the two-dimensional image of the characteristic pattern        in the moved position;    -   (g) storing a coordinate of the stage (Xf, Yf) when the image is        obtained in the step (f);    -   (h) applying a pattern matching between a portion of the image        obtained in the step (c) and the image obtained in the step (f)        to calculate a displacement between the two images in the X- and        the Y-directions (ΔX pixel, ΔY pixel);    -   (i) calculating a difference between the coordinate (Xc, Yc)        stored in the step (c) and the coordinate (Xf, Yf) stored in the        step (f), defined by (Xf−Xc) or (Yf−Yc);    -   (j) calculating a size per pixel, (Xf−Xc)/ΔX or (Yf−Yc)/ΔY, or a        magnification of a projection optical system;    -   (k) storing the size per pixel or the magnification of the        projection optical system, which has been calculated in the step        (j), into a memory;    -   (l) calculating a moving distance of the stage by using the size        per pixel so as to perform the alignment operation;    -   (m) irradiating the beam toward the surface of the substrate;    -   (n) detecting the back-scattered beam containing the information        of the substrate;    -   (o) obtaining an image of the substrate from the detected        back-scattered beam; and    -   (p) performing an inspection of the substrate by using the        obtained image.

According to another aspect of the invention, an apparatus forinspecting a substrate surface is provided, in which a surface of asubstrate having a chip formed therein is inspected by using a beam, foraligning of the chips, the apparatus comprising:

a device for placing the substrate so that the chip is positioned withina field of view subject to the inspection;

a measuring device for measuring a magnification for a detection whenthe chip is positioned within the field of view subject to theinspection;

a calculator for calculating a distance of a position error of the chipbased on the measured magnification for the detection; and

a compensator for compensating for the position of the chip based on thecalculated distance.

According to another aspect of the invention, an apparatus forinspecting a substrate surface is provided, in which a surface of asubstrate having a chip formed therein is inspected by using a beam, forplacing the substrate so that the chip is positioned within the field ofview subject to the inspection, the apparatus comprising:

a measuring device for measuring a magnification for a detection whenthe chip is positioned within the field of view subject to theinspection;

a calculator for calculating a distance of a position error of the chipbased on the measured magnification for the detection;

a compensator for compensating for the position of the chip based on thecalculated distance;

a detector for detecting a back-scattered beam containing theinformation of the surface of the substrate, the back-scattered beambeing emanated from the substrate which has been irradiated by the beamafter the position of the chip is compensated for; and

an image-obtaining device for obtaining an image of the surface of thesubstrate from the detected back-scattered beam, wherein

the obtained image is used to carry out the inspection of the substrate.

According to another aspect of the invention, an apparatus is providedfor inspecting patterns within a plurality of dies located approximatelyregularly along two axial directions that are not parallel with respectto each other on a substrate, the apparatus comprising:

a computing means for generating an equally spaced grid according towhich the dies on the substrate should be virtually placed; and

a means for compensating for a difference in positions of the dies onthe substrate with respect to the target grid.

In the apparatus in accordance with another aspect of the invention, inwhich the means for compensating for a difference in positions of thedies on the substrate with respect to the target grid may comprise:

a means for computing a position error of the die on the substrate withrespect to the target grid; and

a control means for feeding back or feeding forward a compensationsignal to offset the position error to a deflector.

According to another aspect of the invention, an apparatus forinspecting a sample surface is provided, comprising:

a beam irradiation source for irradiating a beam toward a sample;

a means for measuring a size per pixel on the sample within a beamirradiated region by the beam irradiation source;

a computing means for calculating a travel distance of a stage by usingthe size per pixel and performing an alignment operation of the sample;

a detector for detecting a secondary beam that has been emanated fromthe sample by the irradiation of the beam and contains the data on thesurface of the sample; and

a means for obtaining an image of the surface of the sample from thesecondary beam that has been detected by the detector and therebyinspecting the sample.

According to another aspect of the invention, an apparatus forinspecting a surface of a sample having a plurality of dies includingpatterns formed therein is provided, the apparatus comprising:

a means for obtaining information necessary to compensate for thepositions of the dies on the sample surface;

a means for measuring and storing a focusing condition of the samplesurface in an arbitrary location within a region subject to theinspection on the sample surface during obtaining the information;

a beam irradiation source for irradiating a beam toward the surface ofthe sample; and

a lens adapted to be adjustable to satisfy the focusing condition of thesample surface when the beam is moved relative to the region subject tothe inspection.

The apparatus in accordance with another aspect of the invention mayfurther comprise a deflector for compensating for a position error ofthe die when the beam is moved relative to the region subject to theinspection.

According to another aspect of the invention, an method is provided forinspecting patterns within a plurality of dies located approximatelyregularly along two axial directions that are not parallel with respectto each other on a substrate, the method comprising steps of:

-   -   (a) generating a target grid according to which the dies on the        substrate should be virtually placed;    -   (b) determining an actual position coordinate of each die on the        substrate;    -   (c) calculating a position error of the each die with respect to        the target grid;    -   (d) compensating for the position of the image of the each die        to be obtained, based on a value of the position error of the        each die and thus obtaining the image; and    -   (e) performing an inspection of the pattern of the die based on        the image obtained after the position thereof is compensated        for.

In the step (a) of the method in accordance with another aspect of theinvention, the target grid may be generated in such a manner that atleast two dies are selected in each of two axial directions from aplurality of dies formed across a surface of the substrate along the twoaxial directions that are not parallel to each other, and from a pitchbetween selected dies, a virtual pitch per die is determined along eachof the two axial directions, and then based on the virtual pitch, thetarget grid is generated. Further, in the step (a) of the method inaccordance with another aspect of the invention, the target grid may begenerated based on position data contained in CAD data. Yet further, inthe step (e) of the method in accordance with another aspect of theinvention, images of two different dies corresponding to each other maybe compared with each other, and a defect may be detected based on adifference obtained from the comparison. Still further, in the step (e)of the method in accordance with another aspect of the invention, thepattern subject to the inspection and the corresponding patterngenerated according to the CAD data are compared to each other, and adefect is detected based on a difference obtained from the comparison.

In the step (a) of the method in accordance with another aspect of theinvention which depends from claim 17, the two dies on the sample may beselected to thereby detect a pitch between the dies, which is determinedas a first pitch; the first pitch is multiplied by a predeterminedmultiplier, and the thus obtained value is determined as a second pitch;an actual pitch between two dies that are spaced by a distance proximalto the second pitch is detected, which is determined as a third pitch;and a value determined by dividing the third pitch by the multiplier maybe taken as the virtual pitch. Further, In the method in accordance withanother aspect of the invention, the two axes that are not parallel withrespect to each other may represent the X-axis and the Y-axis that areorthogonal to each other. Further, in the step (a) of the method inaccordance with another aspect of the invention, the virtual pitchbetween dies may be determined by using a dicing line parallel to theX-axis or the Y-axis or a predetermined pattern within the die. Yetfurther, in the step (d) of the method in accordance with another aspectof the invention, the position compensation for the image may be carriedout by a deflector for an electron beam.

According to another aspect of the invention, a method is provided forinspecting a surface of a sample, comprising steps of:

irradiating a beam toward the surface of the sample and measuring a sizeon the surface of the sample per pixel within the beam irradiatedregion;

calculating a moving distance of a stage by using the size andperforming an alignment operation of the sample based on a result fromthe calculation; and

irradiating the beam onto the sample and detecting a secondary beam thathas been emanated from the surface of the sample by the irradiation ofthe beam and contains the information of the surface of the sample, andthereby inspecting the surface of the sample.

In the method in accordance with another aspect of the invention, thestep of measuring the size may be carried out by measuring the number ofpixels of a pattern having a known size.

According to another aspect of the invention, a method is provided forinspecting a surface of a sample, comprising steps of:

obtaining information necessary-to compensate for a position of a die onthe surface of the sample;

measuring and storing a focusing condition of the surface of the samplein an arbitrary location within a region subject to the inspectionduring obtaining the information;

irradiating a beam onto the sample;

controlling the beam to make a scanning operation or moving a stage sothat the beam move relative to the region subject to the inspection onthe surface of the sample, while adjusting a lens to satisfy thefocusing condition of the surface of the sample; and

detecting a secondary beam that has been emanated from the sample by theirradiation of the beam and contains data of the region subject to theinspection, and thereby inspecting the surface of the sample.

In the method in accordance with another aspect of the invention, thestep of inspecting the surface of the sample may include a step ofobtaining an image of the region subject to the inspection containing aplurality of pixels by using a CCD or a CCD-TDI and then inspecting thesurface of the sample by comparing thus obtained image with a referenceimage. Similarly, in the method in accordance with another aspect of theinvention, the step of inspecting the surface of the sample may includea step of obtaining an image of the region subject to the inspectioncontaining a plurality of pixels by using a CCD or a CCD-TDI and theninspecting the surface of the sample by comparing thus obtained imagewith a reference image. Further, in the method in accordance with claim29 with another aspect of the invention which depends from anotheraspect of the invention, the step of inspecting the surface of thesample may be carried out, for an area including patterns within a diedefining a cyclic structure, by means of the comparison among the cyclicstructures within the same die, but for an area including patterns notdefining a cyclic structure, by means of the comparison with thereference image. Yet further, in the method in accordance with anotheraspect of the invention which depends from another aspect of theinvention , the step of inspecting the surface of the sample may becarried out, for an area including patterns within a die defining acyclic structure, by means of the comparison among the cyclic structureswithin the same die, but for an area including patterns not defining acyclic structure, by means of the comparison with the reference image.

According to another aspect of the invention, a method is provided forevaluating a sample surface with an electron beam incident to the samplesurface having a plurality of pixels, the method comprising steps of:

-   -   (a) irradiating an electron beam onto a sample and, detecting        secondary electrons or back-scattered electrons;    -   (b) amplifying and A/D converting a detected signal to thereby        form a two-dimensional image containing a density data and        inputting the formed image on a predetermined first region into        a memory;    -   (c) forming a two-dimensional image containing a density data on        a second region expected to contain the same pattern as of the        region whose image has been input in the step (b) and inputting        the formed image into another memory;    -   (d) performing a density matching between the image obtained in        the step (b) and the image obtained in the step (c) and then        increasing or decreasing the density of one of the two images so        as to match the average density between the two images;    -   (e) performing a pattern matching between the images having the        average density matched to each other, calculating a difference        between images to which the pattern matching has been applied,        and then taking the location having the difference as a        candidate for a defect; and    -   (f) obtaining a two-dimensional image of a third region expected        to contain the same pattern as the first and the second regions,        performing a density matching of the two-dimensional image of        the third region with the image of the first or the second        region, comparing to the candidate for the defect obtained in        the step (e), and determining the defect from the candidate for        the defect.

In the method in accordance with another aspect of the invention, theelectron beam may be a multi-beam which consists of a plurality of beamsarranged such that when the plurality of beams is projected in one axialdirection, each beam is equally spaced from adjacent beam, and isadapted to make a scanning operation in a direction orthogonal to theone axial direction, wherein the two-dimensional image may be formed byelectrically controlling the multi-beam so as to make the scanningoperation while moving a sample stage continuously in the directionparallel to the one axial direction. Further, in the method inaccordance with another aspect of the invention, the electron beam maybe a beam having a rectangular shape elongated in one axial direction,wherein the beam is controlled to make a scanning operation along ashort side direction of the rectangular shape while moving a samplestage continuously along a long side direction of the rectangular shapeso as to irradiate the beam onto the sample, and secondary electronsemanated from the sample or back-scattered electrons therefrom aredetected as an image by a projection optical system. Yet further, in thestep (d) of method in accordance with another aspect of the invention,the density matching may be carried out such that firstly offset valuesare matched so that the lowest densities of the two images match eachother and then a gain is adjusted so as for the highest densities of thetwo images to match each other.

According to another aspect of the invention, a device manufacturingmethod is provided, in which a sample in the course of processing orafter having been processed is inspected for any defects by using adefect inspection apparatus in accordance with any one of the aspect ofthe invention.

According to another aspect of the invention, a device manufacturingmethod is provided, in which a sample in the course of processing orafter having been processed is inspected for any defects by using adefect inspection method in accordance with any one of the aspect of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view showing main components of a defectinspection apparatus according to the present invention;

FIG. 2 is a plan view showing main components of a defect inspectionapparatus according to the present invention;

FIG. 3 is a diagram showing a mini-environment unit of a defectinspection apparatus according to the present invention;

FIG. 4 is a diagram showing a configuration of a loader housing of adefect inspection apparatus according to the present invention;

FIG. 5 is a diagram showing a potential applying mechanism in a defectinspection apparatus according to the present invention;

FIG. 6 is a schematic diagram showing a configuration of an electronbeam calibration mechanism in a defect inspection apparatus shown inFIG. 1;

FIG. 7( a) is a schematic diagram showing a projection type electronoptical device of a sample inspection apparatus, with which an alignmentmethod and a defect inspection method using said aligning methodaccording to the present invention can be implemented, and FIG. 7( b) isa pattern diagram showing a mesh for making an electric field uniform;

FIG. 8( a) is a diagram showing a field of view of an electron opticalsystem in the electron optical device of FIG. 7 along with acharacteristic pattern on a wafer, and FIG. 8( b) is a diagram showing astate where the characteristic pattern on the wafer has been movedwithin the field of view by shifting the field of view of the electronoptical system by a certain distance;

FIG. 9( a) is a diagram showing one method for obtaining atwo-dimensional image of the pattern on the wafer surface in theelectron optical device of FIG. 7, while FIG. 9( b) is a diagram showinganother method for obtaining a two-dimensional image of the pattern onthe wafer surface in the electron optical device of FIG. 7;

FIG. 10( a) is a schematic diagram showing a multi-beam type electronoptical device in a semiconductor inspection apparatus of FIG. 1, withwhich an aligning method and a defect inspection method using saidaligning method according to the present invention can be implemented,FIG. 10( b) is a plan view of a multi aperture used therein, and FIG.10( c) is a enlarged view of the circled portion “A” in FIG. 10( a).

FIG. 11 is a schematic diagram showing a multi-anode used in theelectron optical device shown in FIG. 10;

FIG. 12 is a chart for illustrating a density control of atwo-dimensional image;

FIG. 13( a) is a diagram showing a range of field of view of theelectron optical system, a positioning of a plurality of electron beamsand a characteristic pattern on a wafer during executing a defectinspection by using the electron optical device of FIG. 10, and FIG. 13(b) is a diagram showing a state where the characteristic pattern on thewafer has been moved within the field of view by shifting the field ofview of the electron optical system by a certain distance;

FIG. 14 is a schematic diagram showing a third embodiment of a defectinspection apparatus according to the present invention, which employs asingle beam type electron optical device;

FIG. 15 is a diagram for illustrating an inspection of a wafer providedby the defect inspection apparatus shown in FIG. 10 and FIG. 14, whereinFIG. 15(A) shows an entire view of a wafer, while FIG. 15(B) shows anenlarged view of a portion of a die on the wafer;

FIG. 16 is a plan view for illustrating an equally spaced virtual gridand a misalignment of a die that has been induced in the lithographyprocess of the die;

FIG. 17 is a plan view for illustrating another example of an equallyspaced virtual grid and a misalignment of a die;

FIG. 18 is a diagram for illustrating an interpolation for a positioncoordinate of a die;

FIG. 19(A) is a schematic diagram showing a fourth embodiment of asample inspection apparatus according to the present invention, whichemploys an electron optical device of multi-optical axis and multi-beamtype, and FIG. 19(B) is a plan view of a magnifying lens shown in FIG.19(A), while FIG. 19(C) is a plan view of an anode shown in FIG. 19(A);

FIG. 20 is a schematic diagram showing a fifth embodiment of a defectinspection apparatus according to the present invention, in which asample is transmittable for an electron beam;

FIG. 21 is a schematic diagram showing a sixth embodiment of a defectinspection apparatus according to the present invention, in which asample is not transmittable to an electron beam;

FIGS. 22(A) through 22(D) are diagrams for illustrating an operation ofthe defect inspection apparatus shown in FIG. 21;

FIG. 23 is a chart for illustrating a flow of inspection procedure in asemiconductor device manufacturing method;

FIG. 24 is a chart for illustrating a basic flow of inspection procedurein the semiconductor device manufacturing method;

FIG. 25 is a diagram showing a setting of dies subject to an inspection;

FIG. 26 is a diagram showing the setting of an inspection area in thedie;

FIG. 27 is a diagram for illustrating an inspection procedure in asemiconductor device manufacturing method;

FIGS. 28(A) and 28(B) are diagrams for illustrating the inspectionprocedure in the semiconductor device manufacturing method;

FIG. 29 is a diagram showing an example of scanning for a case of asingle die to be inspected in the inspection procedure in thesemiconductor device manufacturing method;

FIG. 30 is a diagram for illustrating a method for generating areference image in the inspection procedure in the semiconductor devicemanufacturing method;

FIG. 31 is a diagram for illustrating a method for comparing one diewith another die adjacent thereto in the inspection procedure in thesemiconductor device manufacturing method;

FIG. 32 is a block diagram for illustrating a system configuration forimplementing the method for comparing one die with another die adjacentthereto in the inspection procedure in the semiconductor devicemanufacturing method;

FIG. 33 is a diagram for illustrating a method for comparing one diewith a reference die in the inspection procedure in the semiconductordevice manufacturing method;

FIG. 34 is another diagram for illustrating the method for comparing onedie with the reference die in the inspection procedure in thesemiconductor device manufacturing method;

FIG. 35 is a flow chart for illustrating the method for comparing onedie with the reference die in the inspection procedure in thesemiconductor device manufacturing method;

FIG. 36 is a flow chart for illustrating a focus mapping in theinspection procedure in the semiconductor device manufacturing method;

FIG. 37 is a diagram for illustrating the focus mapping in theinspection procedure in the semiconductor device manufacturing method;

FIG. 38 is a graphical representation for illustrating the focus mappingin the inspection procedure in the semiconductor device manufacturingmethod;

FIG. 39 is another diagram for illustrating the focus mapping in theinspection procedure in the semiconductor device manufacturing method;

FIGS. 40(A) through 40(C) illustrate the focus mapping in the inspectionprocedure in the semiconductor device manufacturing method;

FIG. 41 is a block diagram showing an embodiment of a defect inspectionapparatus according to the present invention, which has beenincorporated into a manufacturing line;

FIG. 42 is a flow chart showing a semiconductor device manufacturingprocess employing a defect inspection apparatus according to the presentinvention; and

FIG. 43 is a flow chart showing a lithography process in FIG. 42.

DETAILED DESCRIPTION OF THE INVENTION

An aligning method and a method for inspecting a sample by using thesame alignment method according to the present invention will now bedescribed. First of all, with reference to FIGS. 1 through 5, a generalconfiguration of a sample inspection apparatus for embodying the abovedescribed method according to the present invention will be explained,said apparatus serving for inspecting a substrate or a wafer having apatterned surface as an object of the inspection for potential defectsor the like contained therein. It is to be noted that the followingdescription is directed to an example taking the wafer as the sample.

In FIG. 1 and FIG. 2, a sample inspection apparatus 1 for inspecting asample for any defects or the likes comprises: a cassette holder 10 forholding a cassette containing a plurality of wafers “W”; amini-environment unit 20; a main housing 30 defining a working chamber31; a loader housing 40 located between the mini-environment unit 20 andthe main housing 30 and defining two loading chambers; a loader 60 forpicking up the wafer W from the cassette holder 10 and loading it on astage device 50 located within the main housing 30; and an electronoptical device 70 attached to a vacuum housing, all of which arearranged in such a physical relationship as depicted in FIGS. 1 and 2.

The sample inspection apparatus 1 further comprises a pre-charging unit81 located within the main chamber 30 which is under a vacuum condition;a potential application mechanism 83 for applying a potential to thewafer W (see FIG. 5); an electron beam calibration mechanism 87 (seeFIG. 8); and an optical microscope 871 constituting an alignmentcontroller for positioning the wafer W on the stage device 50.

The cassette holder 10 is designed to hold a plurality (two pieces inthis embodiment) of cassettes “c” (e.g., a closed cassette, such as FOUPmanufactured by Assist Inc.), each containing a plurality (e.g., 25pieces) of wafers W placed side by side in parallel with each otheralong the up and down direction. This cassette holder 10 may employ asuitable structure depending on the specific cases selectively such thatfor a case where the cassette is transferred by a robot or the like andloaded onto the cassette holder 10 automatically, a specific suitablestructure therefor may be employed and that for a case where the loadingoperation is manually carried out, an open cassette structure suitabletherefor may be employed.

In this embodiment, the cassette holder 10 has a system forautomatically loading the cassette c, and comprises, for example, anlifting table 11 and an lifting mechanism 12 for moving up and down thelifting table 11, wherein the cassette c is set on the lifting table 11automatically in a state illustrated by the chain line in FIG. 2, andafter having been set, the cassette c is rotated automatically into anorientation illustrated by the solid line in FIG. 2 for heading to anaxial line of rotational movement of a first transport unit (as will bedescribed later) within the mini-environment unit 20, and then thelifting table 11 is lowered down to the position indicated by the chainline in FIG. 1. The cassette holder used in the case of the automaticloading or the cassette holder used in the case of the manual loadingmay appropriately employ any known structures, and detailed descriptionof its structure and function should be herein omitted.

The wafers W contained in the cassette c are those subject to theinspection, and such an inspection may be carried out after or in thecourse of a process for processing the wafer in the series of processesfor manufacturing the semiconductor. Specifically, those wafers thathave experienced the film-depositing step, the CMP step, the ionimplantation step and the like, or those wafers that have been or havenot been patterned on the surfaces thereof may be accommodated in thecassette. A plurality of those wafers W are accommodated in the cassettec so as to be spaced in parallel with each other along the up and downdirection. For this reason, an arm of the first transport unit (as willbe described later) is adapted to move up and down so that the wafer Win a desired position can be held by the first transport unit.

In FIGS. 1 through 3, the mini-environment unit 20 comprises: a housing22 defining a mini-environment space 21 of which atmosphere may becontrolled; a gas circulator 23 for providing the atmosphere control bycirculating a gas such as a clean air within the mini-environment space21; an exhausting device 24 for recovering and then exhausting a portionof the air supplied into the mini-environment space 21; and apre-aligner 25 arranged within the mini-environment space 21 forproviding a coarse alignment of the wafer W subject to the inspection.

The housing 22 comprises a top wall 221, a bottom wall 222 andcircumferential walls 223 surrounding four circumferential portions soas to provide a structure to separate the mini-environment space 21 froman external environment. In order to provide the atmosphere control ofthe mini-environment space 21, the gas circulator 23 comprises, as shownin FIG. 3, a gas supply unit 231 which is attached to the top wall 221within the mini-environment space 21 for cleaning the air and thendirecting a laminar flow of thus cleaned air right below through one ormore gas blowoff openings (not shown); a recovery duct 232 located onthe bottom wall 222 within the mini-environment space 21 for recoveringthe air that has flown down toward the bottom; and a conduit 233interconnecting the recovery duct 232 and the gas supply unit 231 forreturning the recovered air back to the gas supply unit 231.

The laminar flow of the clean air directed downward, or the down flow,is supplied such that it can flow mainly through a conveying surface ofthe first transport unit 61 located within the mini-environment space 21to thereby prevent any dust which could be produced by the transportunit 61 from adhering to the wafer W. An access port 225 is formed in alocation of the circumferential wall 223 of the housing 22 adjacent tothe cassette holder 10.

As shown in FIG. 3, the exhausting device 24 comprises: a suction duct241 disposed in a location lower than the wafer conveying surface ofsaid transport unit 61 and in the lower portion of the transport unit; ablower 242 disposed external to the housing 22; and a conduit 243 forinterconnecting the suction duct 241 and the blower 242. This exhaustingdevice 24 sucks the gas flowing down along the circumference of thetransport unit and containing the dust which could be produced by thetransport unit, through the suction duct 241, and exhausts that air tothe outside of the housing 22 via the conduits 243 and the blower 242.

The pre-aligner 25 disposed within the mini-environment space 21 isdesigned to detect optically or mechanically an orientation-flat formedin the wafer W (referred to a flat portion formed in an outer peripheryof a circular wafer) or one or more V-shaped cut-out or notch formed inan outer peripheral edge of the wafer W, and to provide in advance analignment of the wafer W in the rotational direction around the axisline O₁—O₁ of the transfer unit 61 within an accuracy of ±1 degree. Thepre-aligner 25 is a constitutional part of a mechanism for determining acoordinate of a subject to be inspected, and takes a role in providing acoarse alignment of the subject to be inspected. Since the pre-aligner25 may be of any known structure, description of its structure andfunction should be omitted.

In FIG. 1 and FIG. 2, the main housing 30 defining the working chamber31 comprises a housing main body 32. The housing main body 32 issupported by a housing supporting device 33 loaded on a vibrationinsulating device or a vibration isolating device 37 located on a tableframe 36 and the housing supporting device 33 comprises a framestructure 331 assembled into a rectangular shape. Thus, the housing mainbody 32 is disposed and mounted securely onto the frame structure 331.The housing main body 32 comprises a bottom wall 321 loaded on the framestructure 331, a top wall 322 and circumferential walls 323 connected toboth of the bottom wall 321 and the top wall 322 to surround fourcircumferential portions, thereby isolating the working chamber 31 fromthe outside.

The housing main body 32 and the housing supporting device 33 isassembled in a rigid structure, wherein the vibration isolating device37 prevents the vibration from the floor on which the table frame 36 isinstalled from being transmitted to this rigid structure. An access port325 for taking in and out the wafer is formed in one circumferentialwall among those circumferential walls 323 of the housing main body 32,which is adjacent to a loader housing 40.

The working chamber 31 is designed to be held in a vacuum atmosphere bya vacuum device (not shown) having a known structure. A controller 2 forcontrolling an overall operation of the apparatus is located under thetable frame 36. The working chamber 31 is typically held under apressure in a range of 10⁻⁴ to 10⁻⁶ Pa.

Referring to FIGS. 1, 2 and 4, the loader housing 40 comprises a housingmain body 43 defining a first loading chamber 41 and a second loadingchamber 42. The housing main body 43 comprises a bottom wall 431, a topwall 432, circumferential walls 433 surrounding four circumferentialportions and a partition wall 434 for separating the first loadingchamber 41 and the second loading chamber 42, so that both loadingchambers 41 and 42 may be isolated from the external environment. Anaccess port 435 is formed in the partition wall 434 for passing thewafer W between two loading chambers 41 and 42. Further, access ports436 and 437 are formed in locations of the circumferential walls 433adjacent to the mini-environment unit 20 and the main housing 30,respectively.

As shown in FIG. 4, since the housing main body 43 of this loaderhousing 40 is mounted on and supported by the frame structure 331 of thehousing supporting device 33, this loader housing 40 is also designed tobe protected from any vibrations otherwise transmitted from the floor.The access port 436 of the loader housing 40 and the access port 226 ofthe housing 22 of the mini-environment unit 20 are aligned andinterconnected with each other, and in a connecting point therebetween ashutter system 27 is arranged so as to selectively block thecommunication between the mini-environment space 21 and the firstloading chamber 41.

The access port 437 of the loader housing 40 and the access port 325 ofthe housing main body 32 are aligned and interconnected with each other,and in a connecting point therebetween a shutter system 45 is arrangedso as to selectively seal and block the communication between the secondloading chamber 42 and the working chamber 31. Further, the opening 435formed in the partition wall 434 is provided with a shutter system 46which selectively blocks the communication between the first and thesecond loading chambers 41 and 42 by closing or opening a door 461.Those shutter systems 27, 45 and 46 are designed to provide an airtightsealing to each loading chamber when they are in closed positions.

In the first loading chamber 41, a wafer rack 47 is arranged, whichholds a plurality, for example two pieces, of wafers W in a horizontalstate to be spaced from each other in the up and down direction. Thefirst and the second loading chambers 41 and 42 are adapted to have theatmosphere controlled to be high vacuum condition (in a range of 10⁻⁵ to10⁻⁶ Pa as a vacuum level) by the aid of a well-known vacuum exhaustingdevice (not shown) including vacuum pump, though not shown. In thatcase, the first loading chamber 41 may be held in a lower vacuumatmosphere as a low vacuum chamber, while the second-loading chamber 42may be held in a higher vacuum atmosphere as a high vacuum chamber,thereby providing an effective way to prevent the contamination of thewafer W. Employing such a configuration not only can help transfer thesubsequent wafer W that is accommodated in the loading chamber and is tobe subjected to a defect inspection into the working chamber 31 withoutdelay, but also can help improve the throughput of the defect inspectionand further help maintain the vacuum level in the surrounding of theelectron beam source, which is required to be held in a high vacuumcondition, at as high vacuum conditions as possible.

The first and the second loading chambers 41 and 42 are connected with avacuum exhausting pipe (not shown) and a vent pipe (not shown) for aninactive gas (e.g., purified dry nitrogen), respectively. With thisarrangement, injecting the inactive gas into each loading chamber canprevent an oxygen gas and the like other than the inactive gas fromadhering to the surface of each chamber with the aid of the inactive gasvent.

It is to be noted that in a sample inspection apparatus using anelectron beam according to the present invention, it is important that asubstance represented by lanthanum hexaboride (LaB₆) that can be used asan electron beam source of an electron optical device should not bebrought into contact with oxygen as much as possible after it is heatedup to such a high temperature where the thermal electron is emittedtherefrom in order not to reduce a lifetime thereof. As it is, this canbe ensured by applying the atmosphere control as described above to theworking chamber 31 in which the electron optical device is installed, ina step prior to a transfer operation of the wafer W thereinto.

The stage device 50 comprises: a stationary table 51 located on thebottom wall 321 of the main housing 30; a Y table 52 operatively mountedon the stationary table 51 to be capable of moving in the Y direction(the direction orthogonal to the sheet surface in FIG. 1); an X table 53operatively mounted on the Y table 52 to be capable of moving in the Xdirection (the left and right direction in FIG. 1); a turntable 54capable of rotating on the X table 53; and a holder 55 located on theturntable 54. The wafer W is releasably loaded on a wafer loadingsurface 551 of the holder 55. The holder 55 may have a known structureallowing for the wafer W to be releasably gripped in a mechanical manneror by an electrostatic chuck system.

The stage device 50 is adapted to provide a highly precise alignment ofthe wafer W held in the holder 55 on the loading surface 551 withrespect to the electron beam irradiated from the electron optical devicein the X direction, Y direction and Z direction (i.e., the up and downdirection in FIG. 1) as well as in the rotational direction around theaxial line orthogonal to the supporting surface of the wafer W (i.e., inthe θ direction), by actuating the plurality of tables 51 to 54described above using a servo motor, an encoder and a variety of sensors(not shown).

It is to be noted that the positioning of the wafer W in the Z directionmay be achieved by, for example, making the position of the loadingsurface 551 on the holder 55 to be fine-tunable. In these operations, areference position of the loading surface 551 is detected by a positionmeasuring device employing laser having very fine diameter (laserinterference range finder using a principle of interferometer) and saidposition is controlled by a feedback circuit (not shown) and inassociation with or instead of the above control, the position of thenotch or the orientation-flat of the wafer is measured to detect aposition within a plane and a rotational position of the wafer withrespect to the electron beam, and the turntable is rotated by, forexample, a stepping motor capable of fine angle controlling so as tocontrol the position of the wafer. In order to prevent or minimize, anyproduction of dust within the working chamber 31, the servo motors 521and 531 and the encoders 522 and 532 for the stage device 50 aredisposed external to the main housing 30. It is to be noted that thereference can be set for the signal obtained by inputting in advance therotational position and/or the position in the X- and the Y- directionsof the wafer W with respect to the electron beam to a signal detectingsystem or an image processing system, both of which will be describedlater.

The loader 60 comprises a first transport unit 61 of a robot systemlocated within the housing 22 of the mini-environment unit 20 and asecond transport unit 63 of a robot system located within the secondloading chamber 42. The first transport unit 61 has a multi-joint arm612 capable of rotating around an axial line O₁—O₁ with respect to adriving section 611. The multi-joint arm may employ any arbitrarystructure, and in the illustrated embodiment, the arm 612 includes threeparts operatively joined so as to be movable rotationally with respectto each other. A first part of the arm 612 of the first transport unit61, which is one of the three parts located in the closest position tothe driving section 611, is attached to a shaft 613 which may be drivento rotate by a driving mechanism of known structure (not shown) arrangedin the driving section 611. The arm 612 can rotate around the axial lineO₁—O₁ with the aid of the shaft 613, while it can be extended orcontracted in the radial direction with respect to the axial line O₁—O₁as a whole unit by a relative rotation among the parts. A tip portion ofa third part of the arm 612, which is one of those parts located in theuppermost position, is provided with a gripping device 616 for grippingthe wafer W, which is implemented by a mechanical, electrostatic orother type chuck of known structure. The driving section 611 is allowedto move in the up and down direction by an lifting mechanism 615.

In operation, the arm 612 of the first transport unit 61 is extendedtoward either one of the directions for M1 and for M2 between those fortwo cassettes c held in the cassette holder, and one piece of wafer Waccommodated in the cassette c is placed onto the arm or gripped by thechuck (not shown) attached to the tip portion of the arm 612, so as tobe taken out of it. After that, the arm 612 is contracted into the stateshown in FIG. 2, and then is rotated to and stopped at a position fromwhich it can be extended toward the direction M3 for the pre-aligner 25.As it is, the arm is again extended so as to place the wafer W held bythe arm 612 onto the pre-aligner 25. The arm 612, after the pre-aligner25 having applied a fine-tuning of the orientation of the wafer W,receives the wafer W from the pre-aligner 25 and then the arm 612 isfurther rotated to and stopped at a position in which the arm is allowedto be extended toward the first loading chamber 41 in the direction M4,where it is extended so as to hand over the wafer W to a wafer receiver47 within the first loading chamber 41.

It is to be noted that in a case of gripping the wafer W mechanically,preferably a circumferential edge region defined by a range within about5mm from the circumferential edge of the wafer W should be gripped. Thisis because the wafer W is in its inner surface entirely patterned withdevices such as circuit wirings only excluding the circumferential edgeregion, and accordingly gripping of the wafer W in that patterned regioncould cause a breakage of the device and a defect therein.

The second transport unit 63 has basically the same structure as thefirst transport unit 61, but it is operable so that the transferoperation of the wafer W is performed between the wafer rack 47 and theloading surface 551 of the stage device 50.

In said loader 60, the first and the second transport units 61 and 63carry out the transfer operation of the wafer W as it is held in thehorizontal state from the cassette c held by the cassette holder 10 ontothe stage device 50 located within the working chamber 31 and viceversa. The up and down motions of the arms 612 and 632 of the transportunits 61 and 63 are limited only to the steps where the wafer W is takenout of or inserted into the cassette c, where the wafer W is placed onor taken out of the wafer rack 47, and where the wafer W is placed on ortaken out of the stage device 50. Therefore, even the transfer of such alarge wafer W having a 30 cm diameter, for example, can be carried outsmoothly.

The transfer operations of the wafer W from the cassette c carried bythe cassette holder 10 onto the stage device 50 located in the workingchamber 31 will now be described in order with reference to FIGS. 1through 4. As for the cassette holder 10, a suitable structure may beselectively employed therefor, as already set forth, depending onparticular cases, including one for the manual setting of the cassetteand another for the automatic setting of the cassette. Once the cassettec is set on the lifting table 11 of the cassette holder 10, the liftingtable 11 is lowered by the lifting mechanism 12 and the cassette c isaligned with the access port 225.

When the cassette c is aligned with the access port 225, the cover (notshown) arranged in the cassette c is opened, and at the same time, acylindrical cover is disposed between the cassette c and the access port225 so as to block the interior of the cassette c and the space insideof the mini-environment unit 21 from the external environment. It is tobe noted that in the case where the shutter system for opening andclosing the access port 225 is arranged in the mini-environment unit 20,that shutter system should be actuated to open and close the access port225.

The arm 612 of the first transport unit 61 has been stopped as it isoriented to either of the direction Ml or M2. Assuming that it hasstopped as oriented to the direction of Ml, when the access port 225 isopened, the arm 612 is extended through the access port 225 to receiveone of the wafers W accommodated in the cassette c by its tip portion.Once the receiving operation of the wafer W by the arm 612 is completed,the arm 612 is contracted and, if said shutter system is installed, saidshutter system is actuated to close the access port 225. Then, the arm612 is rotated around the axial line O₁—O₁ and stopped in a positionallowing for the arm 612 to be extended toward the direction M3, wherethe arm 612 is extended and places the wafer W loaded on its tip portionor gripped by the chuck onto the pre-aligner 25, which in turndetermines the orientation of the rotational direction of the wafer W,or the direction around the central axis line orthogonal to the waferplane, to be set within a specified range.

Once the alignment operation has been completed, the first transportunit 61, after having received the wafer W from the pre-aligner 25 ontothe tip portion of the arm 612, contracts its arm 612 and takes aposture ready to extend the arm 612 toward the direction M4. Then, thedoor 272 of the shutter system 27 is moved to open the access ports 226and 436, so that the arm 612 is extended into the first loading chamber41 and loads the wafer W into the upper step side or the lower step sideof the wafer rack 47. It is to be noted that, as described above, beforethe shutter system 27 goes into the open position to allow the wafer Wto be transferred to the wafer rack 47, the opening 435 defined in thepartition wall 434 would have been closed to be airtight by the door 461of the shutter system 46.

In the course of transfer operation of the wafer W by the firsttransport unit 61, clean air flows down in a laminar flow as the downflow from the gas supply unit 231 arranged in the upper side of thehousing 22 of the mini-environment unit 20 so as to prevent the dustfrom adhering to the top surface of the wafer W during its transferoperation. A portion of the air in the surrounding of the transport unit61 is sucked through the suction duct 241 of the exhausting device 24and exhausted to the outside of the housing. This is because a portionof the air supplied from the supply unit 231, for example, about 20%thereof, is mainly contaminated air. The remaining portion of the air isrecovered via the recovery duct 232 disposed in the bottom of thehousing 22 and returned back to the gas supply unit 231.

Once the wafer W has been loaded in the wafer rack 47 within the firstloading chamber 41 by the first transport unit 61, the shutter system 27is actuated into the closed position to close the loading chamber 41.Subsequently, the first loading chamber 41 is filled with an inactivegas to purge the air, and after that said inactive gas is also exhaustedto bring the interior of the loading chamber 41 into the vacuumatmosphere. The vacuum atmosphere of the first loading chamber 41 may beset at a low vacuum level.

Once a certain degree of vacuum has been obtained in the loading chamber41, the shutter system 46 is actuated to open the access port 435, whichhas been closed to be airtight by the door 461, and the arm 632 of thesecond transport unit 63 is then extended into the first loading chamber41 and receives one piece of wafer W from the wafer receiver 47 byplacing it on the tip portion of the arm 632 or by gripping it by thegripping device, such as a chuck, installed in the tip portion of thearm 632. After the receiving operation of the wafer W having beencompleted, the arm 632 is contracted, and the shutter system 46 is againactuated to close the access port 435 by the door 461.

It is to be noted that before the shutter system 46 is actuated into theopen position, the arm 632 takes a posture ready to extend toward thedirection N1 for the wafer rack 47, and further, the access ports 437and 325 have been closed by the door 452 of the shutter system 45 toblock the communication between the second loading chamber 42 and theworking chamber 31 in the airtight condition. Once the access port 435and the access ports 437 and 325 have been closed, the second loadingchamber 42 is vacuum evacuated and ultimately brought into the vacuum ata higher vacuum level than that in the first loading chamber 42.

During this vacuum evacuation of the second loading chamber 42, the arm632 of the second transport unit 63 is rotated to a position in which itis allowed to extend toward the stage device 50 in the working chamber31. On one hand, in the stage device 50 within the working chamber 31,the Y table 52 is moved until the centerline X₀—X₀ of the X table 53approximately comes into alignment with the X-axis line X₁—X₁ crossingthe rotational axial line of the second transport unit 63, while at thesame time the X table 53 is moved to a position closest to the loaderhousing 40 and stands by in this state. When the second loading chamber42 has been brought into the approximately same level of vacuumcondition as the working chamber 31, the door 452 of the shutter system45 is actuated to open the access ports 437 and 325, and the arm 632 isextended into the working chamber 31, such that the tip portion of thearm 632 holding the wafer W comes near to the stage device 50 in theworking chamber 31 and then places the wafer W on the loading surface551 of the stage device 50. When the loading operation of the wafer Whas been completed, the arm 632 is contracted, and the shutter system 45closes the access ports 437 and 325.

The stage device 50 comprises a mechanism for applying an negative-biaspotential (or a retarding potential) to the wafer W. This is a mechanismintended to avoid a failure such as discharging due to a short circuitby way of setting the arm 632 in a potential similar or proximal to thepotential level of the stage device 50 or in a floating potential duringthe arm 632 going to the stage device 50 to pick up or to place thewafer W from or onto the stage device 50. It is to be noted that duringtransferring of the wafer W onto the stage device 50, the bias potentialapplied to the wafer W may be turned off.

In controlling of the bias potential, the potential may be turned offuntil the wafer is transferred to the stage and it may be turned onafter the wafer has been transferred to and placed on the stage so as toapply the bias potential. The timing of the application of the biaspotential may be controlled by a tact time that has been determined inadvance to apply the bias potential, or otherwise by a sensor whichdetects that the wafer has been placed on the stage and transmits adetection signal as a trigger to apply the bias potential. Further, theclosing operation of the access ports 437 and 325 by the shutter system45 may be detected so as to use the detection signal as the trigger toapply the bias potential. Yet further, in case of using theelectrostatic chuck, the chucking operation by the electrostatic chuckmay be detected so as to use the detection signal as the trigger toapply the bias potential.

FIG. 5 shows a mechanism 83 installed in the stage device 50 to applythe negative-bias potential (retarding potential) to the wafer W. Thispotential application mechanism 83 is intended to control the generationof the secondary electrons by applying the potential in a range of ±some V to the platform 551 of the stage on which the wafer W is placed,based on the fact that the secondary electron data emanated from thewafer W (the generation rate of secondary electron) depends on thepotential of the wafer W. Further, this potential application mechanism83 also provides a function for decelerating the original energy of theirradiating electrons so as to irradiate the wafer W with theirradiating electron energy in a range of about 100 to 500 eV.

The potential application mechanism 83 comprises, as shown in FIG. 5, avoltage applying device 831 electrically connected to the loadingsurface 551 of the stage device 50, and a charge-up check and voltagedetermination system (hereinafter, referred to as a check anddetermination system) 832. The check and determination system 832comprises a monitor 833 electrically connected to an image formingsection 765 in a detecting system of the electron optical device 70,which will be described later, an operator 834 connected to the monitor833 and a CPU 835 connected to the operator 834. The CPU 835 supplies asignal to the voltage applying device 831. The potential applicationmechanism 83 is designed to look for a potential that is not likely tocharge the wafer subject to the inspection and applies that potential.

One method for inspecting the wafer W for any electrical defects maytake advantage of the fact that the voltage of the portion to beelectrically insulated in a normal condition varies when it is broughtinto conducting state. This may be achieved by a procedure in whichfirstly, charges are added in advance to the wafer W to thereby producea voltage difference between one portion which is to be electricallyinsulated in a normal condition and has been kept actually in the normalcondition and the other portion which is to be electrically insulated inthe normal condition but has been brought into the conducting state bysome reasons; secondly, the data containing the voltage difference isobtained by irradiating the electron beam to these portions; and thenthe thus obtained data is analyzed to detect that the latter portion hasbeen actually in the conducting state.

The operations during a process for transferring the wafer W in thecassette c onto the stage device have been described, and in the processfor returning the wafer W, which has been placed on the stage 50 andfinished with a predetermined processing, from the stage device 50 backinto the cassette c, the operations as described above should beperformed in the inverse sequence. Further, since the first transferunit 61 can transfer the wafer W between the cassette c and the waferrack 47 while the second transfer unit 63 is transferring another waferW between the wafer rack 47 and the stage device 50 so as to keep the aplurality of wafers loaded in the wafer rack 47, the inspection processcan be progressed efficiently.

The pre-charge unit 81 is arranged within the working chamber 31 in alocation adjacent to an optical column 71 of the electron optical device70, as shown in FIG. 1. The present inspection apparatus employs such asystem in which a device pattern or the like formed in the surface ofthe wafer W is inspected by irradiating the electron beam and scanningthereby the wafer W as an object to be inspected. Accordingly, inoperations, the data of the secondary electrons generated by theirradiation of the electron beam are collected as the data of the wafersurface, wherein depending on the material of the wafer, energy of theirradiated electrons and so on, the wafer surface may be occasionallycharged, or charged-up. In this regard, the wafer surface may possiblyhave some regions that would be charged intensively and other regionsthat would be charged moderately. If the wafer surface is not evenlycharged, then the secondary electron data should be uneven, inhibitingthe accurate data from being obtained. To prevent unevenness, thepre-charge unit 81 having a charged particle irradiating section 811 isprovided. In order to eliminate the uneven charging, prior to theirradiation of the electrons for the inspection onto a predeterminedlocation on the wafer W to be inspected, charged particles areirradiated from the charged particle irradiating section 811 of thepre-charge unit 81. The charge-up of the wafer surface can be detectedby forming in advance an image of the wafer surface to be detected andmaking an evaluation on said image, and based on the detection result,the pre-charge unit 82 may be actuated. In the pre-charge unit 81, theprimary electron beam may be irradiated in its out-of-focus condition.

The defect inspection apparatus 1 shown in FIG. 1 comprises an alignmentcontroller 87. This alignment controller 87 is implemented by anapparatus for aligning the wafer W with respect to the electron opticaldevice 70 by using the stage device 50, and it can provide the controls,as shown in FIG. 8, including a coarse aligning of the wafer W by a widefield observation of the wafer W using an optical microscope 871 in alower magnification than that used in the electron optical device 70, analigning of the wafer W in a high magnification by using an electronoptical system of the electron optical device 70, a focal adjusting, aninspected region setting, a pattern alignment and the like. The reasonthe optical system is used to inspect the wafer W in the lowmagnification is that it is required in order to execute the inspectionof the pattern of the wafer W automatically that the alignment markshould be detected easily by the electron beam when the pattern of thewafer W is observed by using the electron beam to thereby make a waferalignment.

Preferably, the optical microscope 871 is operatively installed withinthe main housing 32 so as to be movable, and a light source (not shown)for actuating the optical microscope 871 is also disposed within themain housing 32. The electron optical system for providing theobservation in the high magnification may share the electron opticalsystems in the electron optical device 70, or a primary optical system701 and a secondary optical system 702. To make an observation in thelow magnification for the point subject to the observation on the waferW, the X-stage 53 of the stage device 50 is moved in the X-direction tobring the point subject to the observation on the wafer into the fieldof view of the optical microscope 871. The optical microscope 871 isused to look at the wafer W through a wide field of view, and theposition on the wafer, which is to be observed, is indicated on amonitor 873 via a CCD 872, based on which the point of observation canbe determined approximately. In this case, the magnification of theoptical microscope 871 may be progressively changed from low to high.

Then, the stage device 50 is moved by a distance corresponding to aspacing δx between an optical axis O₃—O₃ of the electron optical device70 and an optical axis O₄—O₄ of the optical microscope 871 to therebybring the point on the wafer W subject to the observation, which hasbeen previously determined with the optical microscope 871, into theposition in the field of view of the electron optical device 70. In thiscase, since the distance δx between the axial line O₃—O₃ of the electronoptical device 70 and the optical axis O₄—O₄ is known beforehand, onlymoving the point subject to the observation by the distance δx can bringit into the position for visual recognition by the electron opticaldevice 70. It is to be noted that although in this illustration theelectron optical device 70 and the optical microscope 871 are spacedfrom each other only along the X-axial line, they may be spaced bothalong the X- and the Y-axial directions. After the point subject to theobservation is transferred into the visual recognition point of theelectron optical device 70, the SEM image of the point subject to theobservation is taken by the electron optical systems of the electronoptical device 70 in the high magnification, and said image may bestored and/or may be indicated in a monitor via a camera unit.

In this way, after the point on the wafer W subject to the observationis indicated on the monitor by the electron optical system in the highmagnification, a misalignment of the wafer W in the rotational directionwith respect to the revolving center of the turntable 54 of the stagedevice 50, or a misalignment δθ of the wafer W in the rotationaldirection around the optical axis O₃—O₃ of the electron optical system,is detected by using a known method, and also a misalignment of apredetermined pattern in the X- and the Y-axial directions with respectto the electron optical device 70 is detected. Based on thus obtainedvalues of detection as well as separately obtained data of theinspection mark formed in the wafer W or the set of data concerning tothe geometry of the pattern of the wafer W and the like, the operationof the stage device 50 is controlled to provide the alignment of thewafer W.

With understanding of the above explanation, some preferred embodimentsof the electron optical device 70 used in the defect inspectionapparatus according to the present invention will now be described.

FIG. 7 schematically shows a configuration of the electron opticaldevice 70 in the apparatus 1 for inspecting a wafer or a semiconductor,of FIG. 1, and this electron optical device 70 is used to implement amethod for aligning a wafer according to the present invention, and thesame method is in turn used to implement a sample inspection method forinspecting a sample, such as a wafer, for any defects. With reference toFIGS. 7 through 9, preferred embodiments of the wafer aligning method aswell as the sample inspection method using the same wafer aligningmethod according to the present invention will now be described.

In FIG. 7, the electron optical device 70 is represented by the one ofimage projection-type, which comprises: a primary electron opticalsystem (hereinafter, referred to as a primary optical system) 72 thatmakes an electron beam emitted from an electron gun into an ellipticalor rectangular shape (e.g., a rectangle) and irradiates thus shapedelectron beam onto a surface of a wafer W, such as a chip, to beinspected; a secondary electron optical system (hereinafter, referred toas a secondary optical system) 74 that guides secondary electronsemanated from the wafer W, or back-scattered electrons therefrom, alongan optical axis B different from an optical axis A of the primaryoptical system 72; and a detecting system 76 that receives the secondaryelectrons or the back-scattered electrons from the secondary opticalsystem 74, form an optical image of the wafer W and converts saidoptical image into an electric signal.

The primary optical system 72 comprises: an electron gun 721 having athermionic emission cathode (LaB₆ cathode) for emitting an electronbeam; lenses 722 and 723 for focusing the electron beams; a shapingaperture 724 for shaping the focused electron beam into an electron beamhaving a predetermined cross section; and deflectors 725 and 726, all ofwhich are disposed in this order with the electron gun 721 in thetopmost location along an optical axis OA1 having a certain angle withrespect to a direction normal to the surface of the wafer W, as shown inFIG. 7. The primary optical system 72 further comprises: an E×Bseparator 727 for deflecting the electron beam into a direction normalto the wafer W by a field created by an electric field and a magneticfield each crossing at a right angle from each other as well as forseparating the secondary electrons emanated from the sample or theback-scattered electrons therefrom; and two doublet-type objective lenssets 728 and 729, which are disposed in this order along a directionnormal to the surface of the sample.

The secondary optical system 74 serves for guiding the secondaryelectrons or the back-scattered electrons from the wafer W, which havebeen separated by the E×B separator 727, along the optical axis OA2normal to the wafer W into the detecting system 76, and it comprises: adoublet-type lens set 741 for magnifying the secondary electrons or theback-scattered electrons; magnifying lenses 742 and 743; and deflectors744 and 745.

The detecting system 76 comprises: a MCP (Micro-Channel Plate) 761; aFOP (Fiber Optical Plate) 762 with a scintillator applied on its lowersurface for converting the secondary electrons or the back-scatteredelectrons into an image of light; an optical lens 763; and a TDIdetector 784. It is to be noted in FIG. 7 that reference numeral 761designates a mesh serving for making an electric field in a frontsurface of the MCP 7761 uniform, which is designed as shown in FIG. 7(b). In addition, reference numerals 767 and 768 designate meshes,respectively, for making an electric field between the MCP 761 and theFOP 762 uniform. A configuration and an operation of the detectingsystem 76 are well known and a detailed description thereof should beomitted. The MCP 761 and the TDI detector 763 together constitute theimage forming section 765, which has been previously mentioned.

In the electron optical device 70 having the above-describedconfiguration, the electron beam emitted from the electron gun 721 isfocused by the lenses 722 and 723 and irradiated evenly onto the shapingaperture 724. The shaping aperture 724 provides an appropriate shapingoperation so that the cross-section of the electron beam from theelectron gun 721 viewed in the direction normal to the optical axis OA1may be rectangular shape (e.g., the rectangle) and also that theirradiation density may be constant within the field of view “V”consisting of 512 pixels in the Y-direction and 2048 pixels in theX-direction as shown in FIG. 8( a).

The rectangular-shaped electron beam is transmitted through thedeflector 725, 726, deflected by the E×B separator 727 toward thedirection normal to the surface of the wafer W and then controlled bythe objective lenses 728 and 729 so as to irradiate the wafer W,specifically the field of view V thereon. The secondary electronsemanated from the wafer W or the back-scattered electrons therefrom bythe irradiation of the rectangular electron beam are focused by theobjective lenses 729 and 728 into an image on a deflection principalplane of the E×B separator 727, thus to form an enlarged image. Thesecondary electrons or the back-scattered electrons that have beenformed into the image are magnified sequentially by the doublet lens 741and the magnifying lenses 742 and 743 and then introduced into thedetecting system 76. The secondary electrons or the back-scatteredelectrons thus introduced into the detecting system 76 are focused intoan image and amplified on the MCP 761, and converted by the scintillatorinto the signal of light, which are in turn formed into an image of thewafer W. This image is transmitted via the FOP 762, contracted by theoptical lens 763 and then detected by the TDI detector 764 as atwo-dimensional image.

Then a description will now be directed to a method for measuring amagnification of the secondary optical system 74 in the electron opticaldevice 70 of image projection-type shown in FIG. 7. A first method formeasuring the magnification may be implemented by using a Faraday cup,in which the magnification can be determined as R/r when an imageobtained by scanning a hole having a known size of Faraday cup, R,disposed in a corner of the stage device 50, on which the wafer W isloaded, is equivalent to the number of pixels, r. That is, when an imageof a structure having a previously known actual size, for example, theimage of the Faraday cup, is taken, and the number of pixels containedin the image of said structure is counted, an actual size per pixel canbe found, from which the magnification can also be determined.

Another method for measuring the magnification employs a laserinterferometer to take an actual measurement of a travel distance of thestage, which may be performed in accordance with the following sequence.It is to be noted that the unit including the tables 52, 53 and 54 andthe holder 55 is generally referred to as the stage.

(a) The stage is moved so that a dicing line at a corner of the wafer Wor a characteristic pattern (e.g., an L-shaped or cross-shaped pattern)“R” on the wafer W may be brought into the field of view “V” of theelectron optical system (FIG. 8( a)).

(b) The rectangular beam (not a square beam but an oblong beam, in theillustrated embodiment) is irradiated, and the back-scattered electronsor the secondary electrons from the wafer W are detected to obtain thetwo-dimensional image.

(c) The coordinate of the stage (Xc, Yc) at the time when thetwo-dimensional image is obtained in the above step (b) is read by thelaser interferometer and stored.

(d) The stage and thus the characteristic pattern R on the wafer W aremoved by a certain distance in the X-direction within the field of viewV (FIG. 8( b)), so that the characteristic pattern R, from which saidtwo-dimensional image has been obtained, may be observed in a marginallocation of the field of view V.

(e) An operation similar to the step (b) is performed at the position towhich the stage has been moved, and the two-dimensional image of thecharacteristic pattern R in the position to which it has been moved istaken.

(f) The coordinate of the stage (Xf, Yf) at the time when the image istaken in the step (e) is read by the laser interferometer and stored.

(g) A pattern matching is applied between a portion of thetwo-dimensional image taken in the position of said step (b) and thetwo-dimensional image taken in the position of said step (e) to therebycalculate a distance of offset between said two images in the X- and theY-directions (ΔX pixels, ΔY pixels).

(h) Further, a difference between the coordinate (Xc, Yc) stored in saidstep (c) and the coordinate (Xf, Yf) stored in said step (f), which isdefined by (Xf−Xc)nm or (Yf−Yc)nm, is calculated.

(i) From said calculated value, a size per pixel (Xf−Xc)/ΔX (nm/pixel)or (Yf−Yc)/ΔY (nm/pixel) is calculated. This size per pixel defines themagnification.

(j) The size per pixel calculated in said step (i) is stored in amemory.

(k) The steps as defined in said (a) through (j) are performed on thepatterns in at least two locations within the surface of the wafer W,and the magnification is determined by the pattern matching betweenrespective two-dimensional images that have been obtained.

(l) The determined magnification is then used to clarify a relationshipamong the arrangement of the patterns, the rotation of the stagecoordinate, the pattern coordinate, the distance between the patternsand the field of view of the electron optical system on the basis perpixel or per actual size and thus to make an aligning operation so thatthe X- and the Y-axial directions of the wafer W may be aligned with thescanning direction of the electron beam.

A specific aligning method will now be described. After the aligningoperations having been applied sequentially in accordance with the abovesteps (a) to (l), the wafer W is inspected for any defects in theprocedure as defined in the following steps (m) to (q).

(m) The surface of the wafer W subject to the inspection is scanned bythe electron beam with the aid of the combination of continuous movementof the stage and/or the scanning operation of the electron beam, and atwo-dimensional image of the pattern in the inspected surface of thewafer W is obtained from the secondary electrons emanated from the waferW or the back-scattered electrons therefrom.

(n) The two-dimensional image obtained in said step (m) is divided intoa predetermined number of regions (into units of cell region) and storedin a memory.

(o) The operations defined in the above steps (m) and (n) are repeated.

(p) From the two-dimensional images that have been divided into thepredetermined number of regions and stored, those two-dimensional imagesfor the regions (cells) at different locations within-the same chip inthe inspected surface of the wafer W, which are expected to contain theidentical patterns to each other, are selected and compared(cell-to-cell inspection) so as to calculate to find a candidate for adefect.

(q) The two-dimensional image of the region in a different chip on thesample surface, which is expected to contain the same pattern, iscompared with the image of the either one of the regions taken in theoperation (p) (chip-to-chip inspection) so as to determine the defectfrom said candidates for a defect.

In the above steps (l) to (p), a defect inspection result may be derivedthrough the image comparison with reference to the size per pixel storedin the memory in the above step (j).

Turning now to FIGS. 9( a) and 9(b), the scanning operation on the waferW in the above step (m) will be described. Assuming that the region onthe wafer W, on which the image is taken in one time of continuousmovement of the stage, is referred to as a stripe “ST”, the method forscanning the surface of the wafer W subject to the inspection can beperformed by either of the following two methods: a first one as shownin FIG. 9( a), in which the longer side of the rectangular electron beamis defined to be equal to the width of the stripe ST (e.g., the longerside of the electron,beam is oriented to the X-direction of the stripeST), and the two-dimensional image of the pattern on the surface subjectto the inspection is obtained while continuously moving the stage in theY-direction; and a second one as shown in FIG. 9( b), in which thelonger side of the electron beam is oriented to align with the directionof the continuous movement of the stage (i.e., the Y-direction), thetwo-dimensional image is taken by scanning the stripe ST in theX-direction with the aid of the deflector 725 and 726. In the lattermethod, since the section area of the electron beam can be reduced, thebeam current density can be increased, and thus the S/n ratio of thesignal can be made enhanced. Further, changing the optical parametersfor the secondary optical system, such as a condition for an excitationof the lens or the like, in synchronization with the scanning by theelectron beam can help the deflectors to control the orbit of thesecondary electrons or the back-scattered electrons to be orientedcloser to the optical axis B to thereby reduce the aberration.

The description will now be directed to an electron optical device 70 aof multi-beam type in a semiconductor inspection apparatus, with whichan aligning method and a defect inspection method using the samealigning method according to the present invention can be implemented.FIG. 10( a) schematically shows a configuration of the electron opticaldevice 70 a of multi-beam type, while FIG. 10( b) is a plan view of amulti-aperture employed in said device.

In FIG. 10( a), the electron optical system of multi-beam type 70 acomprises a primary optical system 72 a, a secondary optical system 74a, and a detecting system 76 a. The primary optical system 72 a isprovided as an optical system for irradiating an electron beam over apattern, such as a chip, on a wafer W and it comprises: an electron gun721 a for emitting an electron beam; a multi-aperture plate 722 a with aplurality of small holes formed therein in a two-dimensional arrangementfor splitting the electron beam emitted from the electron gun 721 a intoa plurality of electron beams (a multi-beam); an electrostatic lens 723a for focusing said plurality of electron beams; an NA aperture member724 a for defining an NA aperture; an electrostatic lens 725 a fordemagnificating the electron beam having passed through the NA aperturemember 724 a; an electrostatic deflector 726 a; an E×B separator 727 a;a first electrostatic objective lens 728 a; deflectors 729 a and 730 a;and a second electrostatic objective lens 731 a. The elements arearranged in this order, as shown in FIG. 10( a), with the electron gun721 in the topmost location in such an orientation that an optical axisOA1 of the electron beam emitted from the electron gun 721 a should benormal to the surface of the wafer W.

As shown in FIG. 10( b), the multi-aperture plate 722 a is provided witha plurality of small holes formed along a line as spaced equally fromeach other in the Y-direction, and thereby allows the minimum intervalsbetween adjacent two beams to be kept greater than the distance for theresolution of the secondary optical system.

The secondary optical system 74 a comprises an electrostatic magnifyinglens 741 a and a deflector 742 a, which are disposed along an opticalaxis OA2 branched at a predetermined angle from the optical axis OA1 inthe vicinity of the E×B separator 727 a, and serves to guide thesecondary electrons or the back-scattered electrons that have passedthrough the E×B separator 727 a into the detecting system 76 a.

The detecting system 76 a comprises a micro-channel plate (MCP) 761 ahaving channels each corresponding to each of the small holes of themulti-aperture plate 722 a, a multi-anode 762 a, a resistor 763 a, animage forming circuit 765 a including an A/D converter, and a memory 766a. As shown in FIG. 11, the multi-anode 762 a defines an elongatedstructure so as to allow the gas discharged from the MCP 761 a to beexhausted quickly. One end 7621 of each one of the multi-anode 762 a isfixed to a substrate 7620 of ceramics and connected to the resistor 763a and the image forming circuit 765 a via a lead 764 a.

An operation of the electron optical device 70 a of multi-beam typehaving the above-described configuration will now be described. Theelectron beam emitted from a single electron gun 721 a irradiates themulti-aperture plate 722 a. The electron beam passes through a pluralityof small holes formed in the multi-aperture plate 622 a and is shapedinto a plurality of electron beams (a multi-beam) M. The plurality ofbeams is focused by the electrostatic lens 723 a to form a crossover inthe NA aperture 724 a. The electron beams, after having formed into thecrossover, are demagnified by the electrostatic lens 725 a, the firstelectrostatic objective lens 728 a and the second electrostaticobjective lens 731 a, and thereby a plurality of electron beams areirradiated on the sample, each defining a size of 0.1 to 0.05 μmthereon. In this case, each of the electron beams is deflected slightlyby the E×B separator 727 a so that it can pass through the center of thelens in the first electrostatic objective lens 728 a, and furtherdeflected by the deflector 729 a to follow an orbit indicated byreference symbol L1. The electrostatic deflectors 729 a and 730 acontrol in combination the electron beams so as to make the scanningoperation in the X-direction.

The secondary electrons emanated from the wafer W or the back-scatteredelectrons therefrom follow an orbit indicated by reference symbol L2,deflected by the E×B separator 727 a into the secondary optical system74 a and advanced along the optical axis OA2. In this case, the group ofsecondary electrons, after having been focused separately for eachelectron beam and magnified by the second electrostatic objective lens731 a and the first electrostatic objective lens 728 a, is deflected bythe E×B separator 727 a into the secondary optical system 74 a, wherethe electrostatic lens 741 a adjusts the magnification such that theintervals between respective electron beams should be equal to theintervals between respective anodes in the multi-anode 762 a disposedbehind the MCP 761 a. Further, in synchronization with the scanningoperation of the primary electron beam on the wafer W, the deflector 742a provides a compensation to the electron beam so as to be alwaysfocused into an image on the front surface of the multi-anode 762 a (theabove description corresponds to the step (a) defined in claim 33 ofWHAT IS CLAIMED IS). The group of secondary electrons absorbed in themulti-anode 762 a is converted by the resistor 763 a into a voltagesignal, which is amplified and A/D converted to form a two-dimensionalimage in the image forming circuit 765 a, and this two-dimensional imageis stored in the memory 766 a (Step (b)).

This two-dimensional image contains the data of density obtained in afirst region (e.g., the left side end of the field of view), whereinreference symbols S1, S2, S3 and S4 represent the regions having thedensity of 1.0, 0.7, 0.3 and 0.1, respectively.

Subsequently, another two-dimensional image, for example, the one shownin the right-hand side in FIG. 12, having the data of density on asecond region (e.g., a region in the vicinity of the optical axis)expected to contain the same pattern as the region input in said step(b) is formed and input in another memory (Step (c)). In FIG. 12,reference symbols R1, R2, R3 and R4 represent the regions having thedensity of 1.2, 0.9, 0.5 and 0.3, respectively.

Then, the images taken in said steps (b) and (c) are called for from thememories, respectively, and a density matching 7001 is applied betweenthem, wherein the density of one of the image should be increased ordecreased to make an average density matched between said two images(Step (d)). For example, as illustrated in FIG. 12, the density R1, R2,R3 and R4 representing 1.2, 0.9, 0.5 and 0.3 as before the matching ischanged to read 1.0, 0.7, 0.3 and 0.1, respectively, thus enabling thepattern matching 7002 to be applied. As a result of the application ofthe pattern matching 7002, it may be found that the image in theleft-hand side has been shifted by a distance of five-addresses in the-X-direction.

Further, a pattern matching is applied between those images that havematched their average densities, and a difference between the images towhich the pattern matching has been applied is calculated, wherein thelocation defined by the difference may be considered as a candidate fora defect (Step (e)). The defects f1 and f2 can be detected by date bycomparing the density among every one of addresses after the patternmatching.

Lastly, a two-dimensional image of a third region expected to containthe same pattern as said first and said second regions is obtained, andadditionally the density matching is applied between the two-dimensionalimage of the third region and the image of either one of said first orsaid second region, wherein the comparison is made with the candidatefor the defect obtained in said step (e) and the defect is determinedfrom the candidates (Step (f)). In these processes, the defectinspection method of the present invention is carried out.

In the above defect inspection method, the electron beam is themulti-beam which consists of a plurality of beams arranged such thatwhen said plurality of beam is projected in one axial direction, eachbeam is equally spaced from adjacent beam and is adapted to make ascanning operation in the direction orthogonal to said one axialdirection, in which said two-dimensional image is formed by electricallycontrolling said multi-beam so as to make the scanning operation whilemoving the sample stage continuously in the direction parallel to saidone axial direction. Further, in said step (d), said density matchingmay be carried out such that firstly the offset values are matched so asfor the lowest densities of said two images to match to each other andthen the gain is adjusted so as for the highest densities of said twoimages to match to each other.

Further, in the electron optical device 70 a of multi-beam type, thescanning sensitivity may be measured and adjusted appropriately. Aprocedure to achieve this will be described below with reference to FIG.13.

(a) Fist of all, a stage is moved so that a dicing line at a corner ofthe wafer W or a characteristic pattern on the wafer W may be broughtinto a field of view 8200 of the electron optical system of the electronoptical device 70 a. As illustrated in FIG. 13( a), the field of view8200 of the electron optical system encompasses, in this illustratedembodiment, an area defined by 2048 pixels in the X-direction and 50pixels in the Y-direction. A plurality of electron beams M (e.g., fiveof electron beams) is positioned on a circle formed around the opticalaxis OA1 of the primary optical system (indicated by the dashed line inFIG. 10( b)) within the field of view 8200, as described above, andarranged such that when said plurality of electron beams is projected inthe Y-direction, each beam is equally spaced from an adjacent beam. Eachelectron beam is adapted to scan a sub-field of view defined by 2048pixels×10 pixels indicated by reference numeral 8201 or 8202. The waferW includes the characteristic pattern 8204 having a point 8203 withwhich the pattern position in the X- and the Y-directions can bespecified, and the stage is moved so that said characteristic pattern8204 may appear within the field of view 8200.

(b) A plurality of electron beams is irradiated on the characteristicpattern 8204 on the wafer W, and secondary electrons or back-scatteredelectrons from the wafer W are detected to thereby obtain atwo-dimensional image.

(c) The coordinate of the stage (Xc, Yc) at the time when thetwo-dimensional image is obtained in the above step (b) is stored in thememory.

(d) The stage is moved in the X- and the Y-directions by a certaindistance within which the characteristic pattern 8204 does not disappearfrom the sub-field of view 8201 or 8202 covered by a single electronbeam (FIG. 13( b)).

(e) The two-dimensional image of the characteristic pattern is taken atthe position to which it has been moved, and the coordinate of the stage(Xe, Ye) at the time when the image is taken is stored.

(f) A pattern matching is applied between those two-dimensional imagestaken in said steps (b) and (e) specifically onto the parts thereofcontaining the characteristic pattern 8204 to thereby calculate adistance of offset between said two images in the X- and theY-directions (ΔX pixels, ΔY pixels).

(g) A difference between the coordinate (Xc, Yc) stored in said step (c)and the coordinate (Xe, Ye) stored in the step (e), which is defined by(Xe−Xc)nm and (Ye−Yc)nm, is calculated.

(h) A scanning sensitivity in the X-direction, (Xe−Xc)/ΔX (nm/pixel),and that in the Y-direction, (Ye−Yc)/ΔY (nm/pixel) are calculated. It isto be noted that the scanning sensitivity is a value indicating how longa single pixel in the displayed image would be in the wafer W.

(i) The scanning sensibility that has been calculated in said step (h)is stored in a memory. This scanning sensibility provides a value neededin the alignment operation that will be performed later. That is, it isrequired in order to make an alignment operation to thereby cancel themisalignment of the wafer that the distance by pixel representing theindicated misalignment should be converted into an actual distance onthe wafer W by using the scanning sensibility.

After the scanning sensibility is determined in the above steps (a)through (i), the defect inspection of the wafer W may be carried out inaccordance with the following steps.

(j) A series of steps (a) to (e) is applied to the wafer W on at leasttwo locations within the surface to be inspected, respectively, and apattern matching is carried out on the obtained images to estimate arelationship among the stage coordinate, the pattern coordinate and thefield of view of the electron optical system. At this time, a precisevalue of the scanning sensibility is used. After the alignment operationis performed in the above manner, the defect inspection is performed.

(k) A two-dimensional image of the pattern on the surface of the wafer Wsubject to the inspection is taken while moving the stage continuouslyin one axial direction and at the same time controlling the electronbeam so as to make a scanning operation in the other axial direction.

(l) The two-dimensional image obtained in said step (k) is divided intoa predetermined number of regions and stored in a memory.

(m) The operations defined in the above steps (k) and (l) are repeated.

(n) From the two-dimensional images that have been divided into thepredetermined number of regions and stored, those two-dimensional imagesfor the regions within the same chip in the inspected surface of thewafer W, which are expected to contain identical patterns to each other,are selected and compared so as to calculate to find a candidate for adefect.

(o) The two-dimensional image of the region in a different chip on theinspected surface, which is expected to contain the same pattern, iscompared with the image of the either one of the regions taken in thestep (n) so as to determine the defect from said candidates for adefect.

In the above steps (j) to (n), the comparison between the images may beperformed by referring to the scanning sensibility stored in the memoryin said step (i).

FIG. 14 shows schematically a configuration of a third embodiment of anelectron optical device used in a defect inspection apparatus accordingto the present invention, which is generally designated by a referencenumeral 70 b. This third embodiment represents a scanning electronoptical device of single beam type similar to the first embodiment shownin FIG. 7, and is different from the second embodiment shown in FIG. 10in a point that the multi-aperture plate 722 a and the multi-anode 762 a(FIG. 11) are not necessary. Also, the scanning electron optical deviceof single beam type is different therefrom in a point that the detectingsystem 76 b in the device of multi-beam type is replaced with a detector767 b comprising a PIN diode or a scintillator and a photo-multiplier.It is to be noted that in FIG. 14, the same reference numerals are usedto designate the similar components to those in FIG. 10, and descriptionof those components should be omitted.

In the electron optical device 70 b of single-beam type shown in FIG. 7and FIG. 14, in which a single beam is used to detect the data for onepixel, it is only required to detect a signal intensity corresponding tothe number of secondary-electron groups emanated from the surface of thewafer W subject to the inspection, which means that, advantageously thedetecting system can be made simple.

One embodiment of a pattern inspection method according to the presentinvention, which can be implemented by a defect inspection apparatusemploying the electron optical device 70 shown in FIG. 10 or FIG. 14,will now be described.

When an electron beam is irradiated onto a substrate such as a wafercontaining a plurality of dies formed thereon and an image of a patternon that surface to be inspected is obtained, theoretically respectivedies should be arrayed as designed even in the obtained image. However,actually the array of the dies on the formed image could be occasionallydifferent from the array of dies on the wafer due to the distortiongenerated in a stage guide for moving the stage and/or an error in anexposure occurring in the lithography process, as explained previously.Since this situation may cause a problem in the defect inspection whichdepends on the image comparison, it is preferable that the deflectingdirection and/or the deflecting amount of the electron beam should becompensated for by the deflector in the electron optical system in orderto obtain an image containing the array of respective dies correspondingto that on the wafer.

To apply the above compensation, it is necessary to obtain a grid thatcan be used as a reference for the image comparison. That is, what isneeded is to obtain “a target grid” to be used as the reference for theimage comparison. The target grid may be the CAD data created in adesign process, or may be determined from a calculation based on anactual measurement of the position of a die on the wafer. In the lattercase, using the actual die on the substrate, in order to generate thetarget grid, pitches in the X- and the Y-directions between the dies onthe sample are detected and averaged so as to determine the virtualtarget grid. Further, also for the case using the CAD data, a similararithmetic operation may be executed as desired. The thus determinedvirtual target grid is used to carry out the defect inspection.

In fact, for many cases, respective dies may define an equally spacedgrid. One embodiment of a pattern defect inspection method according tothe present invention will now be described specifically, with referenceto FIG. 15 showing a plan view of the wafer 1001, by taking one case asa general example, in which respective dies define the equally spacedgrid, meaning that the target grid represents the equally spaced grid.As shown in FIG. 15, a plurality of dies 1004 are formed on a surface ofa wafer 1001 (15 dies are formed by way of example in FIG. 15), whichare arranged regularly along the X- and the Y-directions orthogonal toeach other. When each of dies 1004 is to be inspected for any defects,preferably the coordinate system on which the dies 1004 are placed andthe coordinate system of the defect inspection apparatus should beaccurately matched to each other. However, in practice, a misalignment(error) in the rotational direction could be occasionally introducedbetween the coordinate system on which the dies 1004 are arranged andthe coordinate system of the defect inspection apparatus, when the wafer1001 is loaded on the stage. Also, the lithography process for creatinga pattern on the wafer 1001 contains a possibility that a misalignmentin a range of some 10 nm to some 100 nm could be induced as compared tothe value defined by the design. The defect inspection method accordingto the present invention allows an accurate defect inspection even insuch cases. A specific procedure of the pattern defect inspection methodaccording to the present invention will now be described.

First, a step for detecting a virtual pitch by using an opticalmicroscope and/or an electron microscope is performed. In this step, itis desired that the detection of the pitch should be carried out in somesteps from a broad range in a low magnification to a narrow range in ahigh magnification. Specifically, the pitch between adjacent dies may bedetected on an enlarged image of the sample (e.g., a distance, P₁,between corresponding corners, “a” and “b”, of the adjacent dies in FIG.15) by using the dicing lines 1005 and 1006. From this, theX-directional pitch between dies can be determined. For the Y-direction,similarly, the pitch between the adjacent dies may be detected.

It is to be noted that since there might be a case where the pitchdetermined for the adjacent dies is significantly different from theactual pitch, in order to improve the accuracy, the pitch between widelyspaced dies is additionally detected, and an average value of thedetected pitches may be determined. This averaging process will bedescribed later. It is to be noted that, instead of detecting an actualpitch between adjacent dies, the data which can be used as a referencesuch as the CAD data created in the design process may be used todetermine the pitch. Further, although the dicing line has been used todetermine the pitch between dies, the application should not be limitedto that. For example, if such a characteristic pattern is selected,which is a predetermined pattern having no similar patterns existing inits surrounding within the same field of view, which could beunintentionally pattern-matched to said pattern, then saidcharacteristic pattern may be used to detect the pitch between diessimilarly to the case with the dicing line. This characteristic patternmay be selected based on the pattern data of the dies, for example.

Subsequently, “an equally spaced virtual grid” is generated. In this“equally spaced virtual grid”, the dies are equally spaced both in theX- and the Y-axial directions. Further, typically the X-axis and theY-axis of said equally spaced grid are orthogonal to each other. The“equally spaced virtual grid” is generated by using the virtual pitchesin the X- and the Y-axial directions that have been detected in theabove manner. In this illustrated embodiment, since the die is arectangle elongated in the Y-axial direction as shown in FIG. 15,therefore the “equally spaced virtual grid” defines a grid having alonger pitch in the Y-axial direction than in the X-axial direction.Thus formed “equally space virtual grid” represents a virtual grid usedas a target for re-arranging the dies that have been actually formedwith uneven pitches to be equally spaced and/or for compensating for amisalignment of a die which could appear in the image for inspection dueto a manufacturing error of the defect inspection apparatus.Accordingly, there would be a probability that the position of theactual die is slightly offset from the position of the die in the“equally spaced virtual grid”.

FIG. 16 shows an “equally spaced virtual grid” defined by the pitch inthe X-axial direction denoted by P_(x) and the pitch in the Y-axialdirection denoted by P_(y). It is to be noted that the “equally spacedvirtual grid” may be a parallelogram, as shown in FIG. 17.

A step for detecting a position coordinate of each die on the wafer willnow be described. The detection of the position coordinate of the diemay be achieved by way of a mark detection by using the electron beam,in which the straight lines represented by the dicing lines 1005 and1006, respectively in parallel with the X- and the Y-axial directions,are used as the marks. The dicing lines 1005 and 1006 to be detected arelocated in the left-hand and the lower sides of the die 1004 in theexample illustrated in FIG. 15(B).

Once the straight line in the X-axial direction 1005 a and the straightline in the Y-axial direction 1006 a of the die 1004 are determinedthrough this mark detection, the position coordinate at the corner ofthe die 1004 (e.g., the lower left corner of the die 1004) may bedetected from an intersection point of the straight lines 1005 a and1006 a. The thus detected position coordinate value at the corner ofeach die 1004 may be stored in a predetermined memory. It is to be notedthat the position coordinate at the corner of each die 1004 may bedetermined for every die on the wafer 100, or otherwise the positioncoordinate may be determined for about one half of the total number ofdies and may be calculated by interpolation for the rest of dies byusing the position coordinates for the adjacent dies.

In this regard, referring to FIG. 18, one example of said interpolationwill be described. If the X-axis and the Y-axis of the stage guide formoving the stage are not precisely orthogonal to each other, theinterpolation may be applied as described below. That is, assuming thatthe coordinates at the lower left corners of the dies D0 and D2, (x0,y0) and (x2, y2), have been determined in advance by the actualmeasurements, the coordinate at the lower left corner of the die D1,(x1, y1), is to be determined. As described above, since thecompensation is to be applied to the case where the X-axis and theY-axis are not precisely orthogonal to each other, the interpolation byway of the linear operation may be applied. As it is, in FIG. 18, sincethe die D1 is expected to be located just in the middle between the dieD0 and the die D2, the x1 and the y1 may be determined by thecalculations: x1=(x0+x2)÷2, and y1=(y0+y2)÷2. Further, a polynomialexpression may be employed when the position coordinate of the die is tobe determined by using the interpolation, which has experienced amisalignment introduced by the combined factors. For example, in a caseusing a quadratic polynomial: (y=ax2+bx+c), as the interpolativeexpression, if there are values of the actual measurements at threelocations: (x10, y10), (x20, y20) and (x30, y30), then variables a, band c can be determined, from which the interpolative expression can bederived.

Subsequently, based on the generated “equally spaced virtual grid” andthe position coordinate of each die on the wafer, the position error foreach die 1004 on the wafer with respect to each corresponding die on the“equally space virtual grid” is calculated. FIG. 16 is a conceptualdiagram for illustrating a case where the die has been formed as it isoffset in the lithography process, in which the “equally spaced virtualgrid” is indicated by the dotted line and each die is represented by arectangle with the solid line. To calculate said position error, firstlythe coordinate system of the generated “equally spaced virtual grid”should be correlated with the coordinate system of the dies at someposition. In the case shown in FIG. 16, the die 1004 a located in thelower left position corresponds to the “equally spaced virtual grid”,but the die 1004 b located in the center among those nine dies is offsetslightly by Δx, Δy in the X- and the Y-axial directions, respectively,from the “equally spaced virtual grid”.

Said position error refers to a difference between the positioncoordinate in the “equally spaced virtual grid” and the correspondingposition coordinate of the die of misalignment, and in FIG. 16, theposition error, Δx and Δy, between the reference coordinate (x₀, y₀) andthe coordinate of the center die 1004 b, (x₁, y₁), is calculated. Thecalculated position error, Δx and Δy, may be stored in a predeterminedmemory.

Subsequently, an actual defect inspection is performed. When the defectinspection is to be performed, an electron beam is irradiated so as toscan the surface of the die 1004, and secondary electron groups emanatedfrom the die 1004 are detected and visualized into an image forinspecting the die for any defects. At this time, since the wafer 1001is loaded on the stage and moved along a predetermined path, if nocompensation is applied, the scanning of the die 1004 of misalignmentmay cause the misalignment also in the image to be obtained.

To solve this problem, the position error, Δx and Δy, which has beendetermined in the above manner is read out of the memory, and acompensation is applied to the deflection of the electron beam so thatthe position error may be cancelled to zero. That is, the direction andamount of deflection of the electron beam is compensated for so that theelectron beam may be irradiated on the point determined from x₁=x₀+Δxand y₁=y₀+Δy.

Alternatively, without using the memory, the variables a, b and c may bederived from the position compensations of the die, (Δx₀, Δy₀), (Δx₁,Δy₁) and (Δx₂, Δy₂) by using a polynomial expression: Δy=aΔx²+bΔx+c, andthen the compensation amount for the deflection may be determined by thecalculation for respective positions of scanning.

Such compensation for the deflection may be carried out by using thedeflector of the electron optical system. For example, in the electronoptical device 70 a of FIG. 10, the position of irradiation of theelectron beam may be compensated for by the deflectors 729 a and 730 a,while the position of the electron beam incident onto the MCP 762 a maybe compensated for by the deflector 742 a. Thus, by applying thecompensation for the deflection to the electron beam M to be irradiatedto the die with position error, resultantly the image of every singledie would be located on the “equally spaced virtual grid”.

As for the misalignment in the X-axial direction, in addition to such afixed one that is generated in the lithography process as describedabove, if the stage guide has a distortion (not shown), there could bealso a misalignment generated during the movement of the stage on whichthe wafer 1001 is loaded. If the stage guide has the distortion, themovement of the stage would not be accurately parallel to the Y-axis butoccasionally make a slight deviation in the X-axial direction. Toaddress this, in the circumstance that the actual position of the stageis kept monitored all the time by a laser interferometer, preferably adifference between this actual position of the stage and the theoreticalposition of the stage may be detected, and the compensation may beapplied to the amount of deflection of the electron beam by thedeflector so that the difference should be cancelled to zero.

Further, as to the compensation for the misalignment in the Y-axialdirection, such a disposition error of the die generated in thelithography process may be compensated for in the same way as describedabove for the error in the X-axial direction. An error from thetheoretical value generated during the movement of the stage may becompensated for in the following manner. For example, assuming that theelectron optical system is actuated by a clock frequency at 100 MHz perpixel, the wafer can be theoretically scanned at a rate of 100pixels/μs. Actually, when the electron beam is irradiated onto thewafer, the electron beam is not irradiated entirely across the die, butthe die is divided into a plurality of elongated areas and each of saidelongated areas is scanned as a unit of scanning operation. This area isreferred to as a “stripe”, which is designated by reference numeral 1002in FIG. 15(A). Since the width of the stripe 1002 in the X-axialdirection has been set to a size for 2048 pixels, as will be describedlater, it takes 20.48 μs for one-time scanning of the stripe 1002 alongthe X-axial direction. Assuming that there is a total injury or losstime of 9.52 μs for the starting and ending in one scanning operation,then the time required for the one-time scanning of the stripe 1002along the X-axial direction is totally 30 μs. Since one pixel length(0.1 μm) of scanning operation is performed along the Y-axial directionwithin said time period, the speed of the stage for making a continuousscanning along the Y-axial direction is calculated as 0.1 μm/30 μs=3.3mm/s. Thus, this value is taken as an average speed of the stage alongthe Y-axial direction, and a relationship between the time and thetheoretical position of the stage is calculated and a result is storedin a memory. On one hand, the actual position of the stage is kept undermonitoring all the time by using a laser interferometer. Owing to thiscircumstance, since any fluctuation in the speed of stage can bedetected from a comparison between said calculated position of the stageand the actual position of the stage, if any position error due to thefluctuation in the speed of stage along the Y-axial direction isdetected, feed-back or feed-forward operation may be applied to thedeflector of the electron optical system in order to cancel thisposition error.

In this way, after the “equally spaced virtual grid” is determined andthen the position coordinate of each die on the wafer having beencompensated for, the defect inspection is now performed. To determine adefect, a plurality of images for the regions expected to contain theidentical patterns are extracted from the obtained images. For example,a plurality of images for the respective stripes 1002 shown in FIG.15(A) are extracted. Then, the extracted images are compared to oneanother, wherein if the images are not precisely matched, it isdetermined that a defect exists. A specified technique for thedetermination will be described later.

Applying the compensation as described above may help generate an imagefor a precise region, and so even in the case of the cell-to-cell ordie-to-die image comparison, only creating of the offset images to theextent of ±2 pixels can provide the defect inspection with asatisfactorily high precision.

A variation of a method for detecting a pitch between dies will be nowdescribed. This time, firstly the pitch between dies 1004 located in thecentral region of the wafer 1001 is detected. For example, an intervalbetween the corners “a” and “b” in FIG. 15(A) is detected. This intervalis taken as a first pitch P1. Subsequently, the first pitch P1 ismultiplied by a predetermined integer, and a resultant value is taken asa second pitch P2. For example, the first pitch P1 is multiplied by 4,or P2=4P1. Subsequently, two dies are selected, which are spaced by adistance proximal to the determined second pitch P2, and the actualpitch between them is detected, which is in turn taken as a third pitchP3. In FIG. 15(A), the distance between the points, “c” and “d”,represents the third pitch P3. This third pitch P3 is divided by saidpredetermined integer to thereby determine a virtual pitch between dies.The above steps are applied to the X- and the Y-axial directions so asto determine the pitches between dies in both directions, or Px and Py(see FIG. 16). By way of such a process, the values Px and Py, which maybe more proximal to the actual pitch between dies, can be determined.

The dividing operation of the die into stripes will now be described. Asalready described, in the actual defect inspection, each die 1004 isvirtually divided into a plurality of stripes 1002, 1003, each extendingin a direction parallel to the Y-axis. This stripe defines a unit ofscanning operation in the X-axial direction by the electron beam E whenthe defect inspection is performed. The width of a single stripe in theX-axial direction has been set to a size for 2048 pixels, for example,wherein if one pixel corresponds to 100 nm (0.11 μm) on the wafer, thewidth of the stripe is 204.8 μm.

Although the size of the die 1004 in the X-axial direction is notnecessarily the integer-multiple of the width of the stripe, 204.8 μm,the width of the stripe 1002 may be set such that the integer-multipleof the width of the stripe may be equal to the width of the die 1004 inthe X-axial direction, or the last stripe 1003 may be the one having areduced width. In dividing the die into stripes, however, the die shouldbe divided such that the patterns at the identical locations on all ofthe dies 1004 should be included in the corresponding identical stripes.

A defect determination as described previously will now be described indetail. As stated above, in determination of a defect, the images of thestripes 1002 located on the different dies but corresponding to eachother are compared. This is because the corresponding stripes areexpected to contain identical patterns to each other if no defectexists, but a mismatch should be found in the result from the comparisonif any defect exists.

In FIG. 15(A), when the defect inspection is carried out by comparingthe patterns in the stripes 1002 on the adjacent dies on the same waferto each other, the stage is moved continuously in the Y-axial directionto thereby enable a sequential observation of the two patterns to becompared, thus helping complete the inspection across the entire surfaceof the wafer in a shorter time.

In an alternative defect inspection technique, the CAD data may be used,for example. In this technique, the same pattern as that contained inthe stripe 1002 is generated as a reference image onto a memory by anarithmetic operation from the CAD data for generating the patterncontained in the stripe 1002, and said reference image is compared tothe pattern on the wafer (the image for the stripe 1002 in FIG. 15(A))to determine a difference therebetween, from which a defect may bedetected.

In the technique for making a comparison between the patterns of twodies, in a case of performing the inspection across the entire surfaceof the wafer, the identical patterns on the dies adjacent to each otheron a wafer are compared and examined sequentially thus making theinspection time shorter. In contrast to this, in the technique formaking a comparison with the reference image obtained from the CAD datacomprises: a step of converting a vector data representing the CAD datato a cluster data representing the image data, storing that image datainto a memory, and generating the reference image; a step of making animage conversion of such a portion that is predicted to contain adifference in its image subject to the inspection from the referenceimage but contains no defect, for example, a corner of a pattern, andreflecting said converted image to the reference image, in order toavoid the detection error; a step of converting the density of thereference image into a density predicted to appear when the imagesubject to the inspection is obtained from the wafer; and a step ofaligning the position of the reference image with the position of theimage subject to the inspection, which has been obtained from the wafer.Either one of the above defect inspection techniques allows detection ofa shape defect or a particle in the pattern, and further, since theelectron beam is used to obtain the image on the wafer, voltage contrastdata can be also obtained to help favorably detect any electricaldefects.

The pattern defect inspection method that has been described above maybe implemented in the electron optical device 70 according to theembodiment shown in FIG. 7, which has been described already, or in adefect inspection apparatus equipped with an electron optical deviceemploying an alternative type of electron optical system illustrated inFIG. 19.

FIG. 19(A) schematically shows the configuration of a fourth embodimentof an electron optical device 70 c used in a defect inspection apparatusaccording to the present invention, and said electron optical device 70c employs an electron optical system of multi-optical axis andmulti-beam type. Each set of the electron optical systems in theelectron optical device 70 c comprises an electron gun 1061, amulti-aperture plate 1062, a condenser lens 1063, an objective lens1065, an E×B separator 1064, a secondary electron image magnifying lens1067, a MCP 1068 and a multi-anode 1069, in which two or more sets ofthose components are arranged in a line so as to face to the wafer 1066.As a result, respective optical axes of the primary optical systems ofrespective sets would be set in the identical positions of thecorresponding stripes on the different dies.

Each of optical components of the primary optical system represented bythe objective lens 1065 or an anode 1061 a is designed to define aplurality of optical elements by forming a plurality of through holesworking as optical axes penetrated through a single sheet of ceramicshaving a coefficient of thermal expansion approximately equal to zeroand aligning it with a knock hole 1071, as shown in FIG. 19(B). In caseof the objective lens 1065, metal coating is selectively applied to aninner side of an electrode hole 1072 and a vicinity of the optical axisso as to prevent charging and to allow an independent voltage to beapplied to the surrounding of each electrode hole 1072, as well.

As illustrated in FIG. 19(C), also in case of the anode 1061 a, sincethe metal coating is applied to the periphery of each anode hole 1074 soas to allow the voltage to be applied independently, an anode current isadjustable individually for each anode hole. The intervals between thoseanode holes 1074 are designed so as to match precisely with theinteger-multiple of the pitch between dies on the wafer 1066 in theX-axial direction, and owing to this, the electron beam passing througheach anode hole can inspect an identical location in the correspondingstripe of the different die. It is to be noted that the anode 1061 a isadapted to adjust its position by rotating around an axis passingthrough the center of the wafer 1066. Once the position error resultantfrom the fluctuation in the moving speed of the stage and/or the errorresultant from the misalignment of the die has been calculated in asimilar manner to that described with reference to the first and thesecond embodiments of the present invention, the feed-forwardcompensation is applied to a deflector 1075 and an electrostaticdeflector 1076 in the E×B separator 1064, so that two dimensional imagesfor regions containing the identical patterns formed therein indifferent dies can be obtainable all the time. Even in case of theoccurrence of misalignment from another factor that could drift the beamposition, since a total of 25 images consisting of 24 images that havebeen taken by shifting from the position of previously obtained image inthe X- and the Y-axial directions by up to ±2 pixels plus one image thathas not been shifted is sequentially compared to the obtained image, noproblem would arise.

FIG. 20 schematically shows a configuration of a fifth embodiment of anelectron optical device 70 d used in an defect inspection apparatusaccording to the present invention, in which a sample to be inspected isa stencil mask transmittable for an electron. A configuration of thedefect inspection apparatus of FIG. 20 together with an inspectionmethod executable in said apparatus will be described in combination. InFIG. 20, an electron beam is emitted from an electron gun 1084comprising a cathode made of LaB₆ 1081, a Wehnelt 1082 and an anode 1083along an axis “Z”. The emitted electron beam is irradiated on arectangular shaping aperture 1085, where it is formed appropriately todefine a rectangle in a cross section vertical to the axis Z. Theelectron beam that has passed through the shaping aperture 1085 to beformed into the rectangular shape is then focused by a condenser lens1086 and forms a crossover in an NA aperture 1087. The electron beam,after passing through the NA aperture 1087, forms a rectangular image ona stencil mask 1089, representing a mask to be inspected, by anirradiation lens 1088.

It is to be noted that the stencil mask 1089 is secured fixedly to astage 1091 with its periphery chucked by an electrostatic chuck 1090. Inorder to measure the position of the stage 1091 all the time, theapparatus is provided with a laser measuring machine comprising astationary mirror 1092, a movable mirror 1093, a stationary half-mirror1094, a laser oscillator 1095 and a laser receiver 1096, in which themovable mirror 1093 is adapted to move in association with the movementof the stage 1091. Owing to this configuration, the laser measuringmachine is operable to determine the position of the stage 1091 based ona difference between a time necessary for a laser light emitted from thelaser oscillator 1095 to be reflected by the fixed mirror 1092 and toreturn to the laser receiver 1096 and a time necessary for the laserlight emitted from the laser oscillator 1095 to be reflected by themovable mirror 1093 and to return to the laser receiver 1096. The resultfrom this measurement is used to measure the position of the stage 1091with high accuracy and thus accomplishes a registration of the stencilmask 1089. This registration will be described later in detail.

Thus, the electron beam emitted from the electron gun 1084 istransmitted through the stencil mask 1089, formed and magnified into animage on a principal plane of an objective lens 1097, further magnifiedby a two-step of magnifying lenses 1098 and 1099 and then enters ascintillator 1100. The scintillator 1100 converts the entering electronbeam into a corresponding image of light, and thus converted image oflight, after having been formed into an image by an optical lens 1101,is further converted into an electric signal by a TDI detector 1102. Byprocessing this electric signal, a two-dimensional image involved in oneregion subject to the inspection on the stencil mask 1089 can beobtained.

A series of the above-described processes is applied to a row of areassubject to the inspection on the stencil mask 1089 while moving thestage 1091 in one direction and also while emitting the electron beamfrom the electron gun 1084. Then, the stage 1091 is shifted so that theelectron beam may be irradiated onto a next row adjacent to theinspected row of areas subject to the inspection, and thereby thetwo-dimensional image is obtained from the TDI detector 1102.Subsequently, similar steps are repeated to obtain the two-dimensionalimages on the entire region subject to the inspection, and thus obtainedtwo-dimensional images are sequentially processed to thereby provide thedefect inspection of the stencil mask 1089.

A registration of the stencil mask 1089 will now be described. In orderto perform the registration, firstly two patterns spaced by a knowninterval on the stencil mask 1089 are brought into the field of view totake a two-dimensional image thereof. After the two-dimensional image isobtained in the above manner, a magnification at the time when theregion on the stencil mask 1089 subject to the inspection appears in thetwo-dimensional image is measured and stored. This stored magnification,said interval and the number of pixels existing within said interval areused to calculate a size per pixel, α, (nm/pixel), which is stored, aswell.

Then, the stage 1091 is moved and the two-dimensional images of thepatterns at two different locations on the stencil mask 1089 areobtained, wherein the position of the stage 1091 at the time when eachof the two-dimensional images has been taken is measured by theabove-described laser measuring machine and stored. Consequently, fromthe thus obtained two-dimensional images, the respective positions ofthe stage and said size, α, a positioning of the stencil mask 1089 andits reference position can be determined accurately. The registration isthus completed.

Thus, the two-dimensional image of improved S/N ratio can be obtained byintegrating the image signal along the direction of the movement of thestage 1091, said image signal having been obtained in association withthe movement of the stage 1091 by the TDI detector 1102 whilecontinuously moving the stage 1091 in one direction along the pattern onthe stencil mask 1089 based on the registration that has been determinedas described above. Once the scanning of the one row of the areassubject to the inspection is completed in this way, the next rowadjacent to the scanned row is then scanned in a similar manner toobtain a two-dimensional image thereof. The TDI detector 1102 caninspect the pattern on the stencil mask 1089 for any defects existingtherein by comparing the obtained two-dimensional image with that of thereference pattern accumulated in the memory (not shown) of the computer.

As described above, since in the fifth embodiment of the presentinvention, the size per pixel, α, determined in the above-designatedprocedure is used prior to the registration, therefore accurateregistration can be achieved even if the magnification varies. It is tobe noted that if the magnification goes out of the acceptable range, themagnification may be adjusted to the acceptable value by zooming themagnifying lenses 1098 and 1099.

FIG. 21 is a diagram schematically showing a configuration of a sixthembodiment of an electron optical device 70e used in a defect inspectionapparatus according to the present invention. In FIG. 21, the object tobe inspected is a wafer of non-transmittance. The configuration of thesixth embodiment will be described below in combination with aninspection procedure executed in the apparatus. In FIG. 21, an electronbeam emitted from an electron gun 111, in which a thermionic emissioncathode is operated in the space-charge-limited condition, is shapedinto a rectangle by a condenser lens 113, an irradiating lens 114, abeam shaping aperture (not shown) and an NA aperture (not shown), all ofwhich are disposed along an optical axis 1112 of a primary opticalsystem, and the shaped beam now enters an E×B separator 1115. Then, anadvancing heading direction of the electron beam is deflected from theoptical axis 1112 to a direction vertical to the wafer, and the electronbeam passes through an objective lens doublet consisting of a firstobjective lens 1117 and a second objective lens 1118 for irradiating thewafer 1116. Similarly to FIG. 20, the wafer 1116 is fixedly secured to astage (not shown), and the position of the stage is observed by a lasermeasuring machine (not shown).

Secondary electrons emanated from the wafer 1116 by the irradiation ofthe electron beam is magnified by the first objective lens 1117, thesecond objective lens 1118 and a image projection optical systemcomposed of three magnifying lenses 1119, 1120 and 1121. The thusmagnified electron beam is detected by a TDI detector 1122 having asensibility to the electron beam and converted to the correspondingelectric signal. This electric signal is supplied to an image formingcircuit 1123, and a two-dimensional image corresponding to the secondaryelectrons emanated from the wafer 1116 is formed. This two-dimensionalimage is accumulated in a pattern memory 1124.

The description will be now directed to how to obtain thetwo-dimensional images from an entire area subject to the inspection ofthe wafer 1116. In FIG. 21, assuming a coordinate system that takes theoptical axis 1125 of the secondary optical system as the Z-axis, definesthe X-axis to be normal to the Z-axis and parallel to the sheet surfaceof FIG. 21, and defines the Y-axis to be normal to both the Z- and theX-axes, the electron beam emitted from the electron gun 1111 is shapedinto a rectangle as described above to irradiate a rectangular area 1131elongated in the Y-axial direction on the surface of the wafer 1116(i.e., a shaded portion in FIG. 22(A)). This area 1131 is, inassociation with the deflecting operation of the electron beam by thedeflectors 1126 and 1127, moved in the X-axial direction by a distancecorresponding to a width 1132 of a stripe of the pattern formed on thewafer 1116. This allows the segment elongated in the X-axial direction(referred to as a scanning field) 1133 on the surface of the wafer 1116to be scanned, while at the same time, the wafer 1116 is movedcontinuously in the Y-axial direction along with the stage. In thismanner, a single stripe on the wafer 1116 is scanned in the X- and theY-axial directions, and in association with this scanning, an image ofthe secondary electrons emanated from the wafer 1116 is obtained, thuscompleting the scanning of said stripe. Then, the stage is shifted inthe X-direction by a distance equal to the width of a single stripe, andthe scanning of the next stripe is carried out so as to take the nextimage.

Since the surface of the wafer 1116 is not necessarily flat, in theillustrated sixth embodiment of the present invention, a focusingcondition on the sample surface has been measured and stored prior tothe image taking. To measure this focusing condition, in one example, adensity distribution over the surface of the wafer 1116 is observed. Toachieve this, the image in the scanning field 1135, which contains anadequate pattern 1134, is obtained within the surface of the wafer 1116,as shown in FIG. 22(B), to thereby measure the density distribution inthe X-axial direction. It is herein assumed that the result is themeasured density distribution 1136 shown in FIG. 22(C). Then, a distanceΔx in the scanning field 1135 corresponding to a rise-up of the densityfrom 12% to 88% is calculated. This distance Δx is calculated at eachtime when a voltage V₄₈ applied to the objective lens 1118 is changed soas to obtain a characteristic curve 1137 indicating a relationshipbetween the Δx and the V₄₈ as shown in FIG. 22(D), and then a voltagevalue V₄₈(min) applied to the objective lens 1118 where the curve 1137indicates a minimum value is determined. Thus, the voltage value for oneof the scanning field is determined. Such an operation is applied to theentire area subject to the inspection on the wafer 1116, and therebyrespective scanning fields and the voltage values V₄₈(min) for thesescanning fields are determined.

Then, the registration of the wafer 1116 is performed in a similarprocedure as described with reference to FIG. 20. First of all, twopatterns with a known interval on the sample are introduced into asingle field of view and a two-dimensional image is taken. After thetwo-dimensional image is obtained in this manner, a magnification at thetime when the region subject to the inspection on the wafer 1116 appearsin the two-dimensional image is measured and stored. This storedmagnification, said interval and the number of pixels existing in thisinterval are used to calculate a size per pixel α(nm/pixel) in the wafer1116, which is also stored.

Then, the stage is moved and the two-dimensional images of the patternsat two different locations on the wafer 1116 are obtained, while theposition of the stage at the time when each of the two-dimensionalimages is taken is measured by the above-described laser measuringmachine and stored. Consequently, from thus obtained two-dimensionalimages, the respective positions of the stage and said size α, thepositioning of the wafer 1116 and its reference position can bedetermined accurately. The registration is thus completed.

Since the size per pixel α, determined in the above-designated procedureis used to perform the registration, accurate registration can beachieved even if the magnification varies. It is to be noted that if themagnification goes out of the acceptable range, the magnification may beadjusted to the acceptable value by zooming the magnifying lenses 1120and 1121.

Thus, the two-dimensional image of which S/N ratio is improved can beobtained by integrating the image signal along the direction of themovement of the stage, said image signal having been obtained inassociation with the movement of the stage by the TDI detector 1122while continuously moving the stage in one direction along the patternon the wafer 1116 based on the registration that has been determined asdescribed above. Once the scanning on one row of the areas subject tothe inspection is completed in this way, the next row adjacent to thescanned row is then scanned in a similar manner to obtain atwo-dimensional image thereof. The TDI detector 1122 can inspect thepattern on the wafer 1116 for any defects existing therein by comparingthe obtained two-dimensional image with that of the reference patternaccumulated in the memory (not shown) of the computer. In this way, whenthe two-dimensional image of the wafer 1116 is to be obtained, in eachscanning field, or in each position of the stage, the excitation voltageof the objective lens 1118 is set to the previously determined voltagevalue, V₄₈(min). This allows the two-dimensional image to be obtainedunder a condition where the lens in the image projection optical systemsatisfies the focusing condition thereof.

It is to be noted that the fifth and the sixth embodiments according tothe present invention are not limited to those described above. Forexample, in the case of the electron optical device having theconfiguration as shown in Fig, 21, a description has been given, by wayof example, to the procedure for setting the lens to satisfy thefocusing condition to take the two-dimensional image from the sample ofnon-transmittance, such as a wafer, but even in the case of atransmittable sample represented by a stencil mask, the electron opticaldevice having the configuration as shown in FIG. 20 may be used to setthe lens to satisfy the focusing condition by executing the similarprocedure.

Turning now to FIG. 23, an inspection procedure in an inspection processof a wafer will be explained. For the reason that a defect inspectionapparatus using an electron beam is typically expensive and itsthroughput is relatively low as compared to other processingapparatuses, in the current circumstances, it is used after theessential processes considered to need the inspection most (e.g., theetching, the film deposition or the CMP (Chemical Mechanical Polishing)flattening processes), or in the wiring process especially in the finepitch wiring process, or the first and second wiring processes and agate wiring process prior thereto.

The wafer to be inspected is, after having been aligned on anultra-precision X-Y stage via an atmospheric transfer system and avacuum transfer system, fixed by an electrostatic chuck mechanism or thelike, to which the defect inspection or the like may be applied inaccordance with a procedure shown in FIG. 23. Firstly, an opticalmicroscope is used to perform a position recognition of each die and/ora detection of height of each location, as desired, which are thenstored (Step 1141). The optical microscope additionally takes any otheroptical microscopic images of desired locations, such as defects whichmay be also used in the comparison with an electron beam image.Secondly, information on recipe in association with the type of wafer(e.g., after which process?, wafer size 200 mm? or 300 mm? and so on) isinput to the apparatus (Step 1142), and then, after completing the stepsof specifying an inspection site (1143), setting an electron opticalsystem (Step 1143) and setting an inspection condition (Step 1144) andso on, a defect inspection is performed while executing the imagetaking, typically in real time. The cell-to-cell comparison, die-to-diecomparison and the like may be executed for inspection by a high-speedinformation processing system containing an algorithm, and the resultmay be output to a CRT or the like and/or stored in a memoryappropriately as desired.

The defect may include a particle defect, an abnormal shape (a patterndefect), an electrical defect (including disconnection in a wiring or avia and bad conduction) and so on, and those defects can bedistinguished and/or the classification of the size of the defect andthe identification of a killer defect (a serious defect making the chipno longer usable) can be carried out at real time. The detection of theelectrical defect may be achieved by detecting an abnormal contrast. Forexample, the location of bad conduction can be distinguished from thelocation of normal conduction from the fact that the former is typicallycharged to be positive by the irradiation of an electron beam (at about500 eV) and thereby the contrast is deteriorated. As an electron beamirradiation means for applying the charge, a low potential (low energy)electron beam generating means (for emitting thermion, UV/photoelectron)may be installed for emphasizing the contrast owing to a potentialdifference, in addition to an electron beam irradiating means used for atypical inspection. Prior to the irradiation of the electron beam forthe inspection onto a region subject to the inspection, this lowpotential (energy) electron beam is generated and irradiated thereto. Inthe case of the image projection method, which can charge the wafer tobe positive by irradiating the electron beam for the inspection onto thewafer, depending on the specification thereof, the electron beamgenerating means of low potential need not be installed additionally.Further, the defect can be detected from a difference in contrast(resultant from a difference in flowability depending on the forward orbackward direction of the device) caused by applying a positive ornegative potential relative to a reference potential to a sample such asa wafer. This is applicable to a line width measuring apparatus and anoverlay accuracy measuring, as well.

The inspection of a sample, such as a wafer, by using an electron beamcan be performed in accordance with a basic procedure as shown in FIG.24. Firstly, in Step 1151, the wafer is introduced onto a stage by atransfer mechanism. Typically, a plurality (e.g., 25 pieces) of wafersto be inspected are accommodated in a cassette holder and one or more ofthem are simultaneously taken out of it and mounted on the stage of adefect inspection apparatus, wherein, since the defect inspectionapparatus is installed in a housing kept in a vacuum condition, a devicefor interfacing between the atmosphere and the vacuum is necessary inorder to carrying out the operation for taking the wafer subject to theinspection out of the cassette holder and mounting it on the stage andthe operation for taking the wafer having finished with the inspectionout of the housing. To this end, when the wafer is to be introduced, thewafer that has been taken out of the cassette holder is firstly cleanedin a mini-environment unit and then transferred into a loading chamber.Since the loading chamber is coupled with the housing via a shutter,once the wafer is transferred into the loading chamber, the loadingchamber is evacuated into vacuum. After the loading chamber is evacuatedto vacuum, the shutter is opened so as to allow a communication betweenthe loading chamber and the housing, wherein the wafer finished with theinspection is removed from the stage and taken out of the housing, whileat the same time, another wafer to be inspected is transferred from theloading chamber to the housing and then loaded on the stage.

Next, in step 1152, an aligning operation is performed so as to make thewafer aligned. When the wafer is loaded on the stage from the loadingchamber, usually, the X- and the Y-axes of a die on the wafer are not inconformity with the moving direction of the stage or the scanningdirection of the electron beam. In this condition, in order to performan accurate inspection for the die on the wafer, firstly the wafer isrotated on the stage to compensate for an angular misalignment of thedie so that the axes defining the die on the wafer are matched with themoving direction of the stage or the scanning direction of the electronbeam. This operation is referred to as an alignment operation.

After the alignment operation of Step 1152, Step 1153 for creating therecipe to set a condition or the like on the inspection is performed. Atleast one type of recipe is necessary for the wafer subject to theinspection, while in order to satisfy a plurality of conditions on theinspection, occasionally a plurality of recipe may be prepared for asingle wafer subject to the inspection. Further, if there is a pluralityof wafers subject to the inspection, which have identical patterns, onlyone recipe may be used for the inspection of said plurality of wafers.In the case of the inspection using the previously created recipe, it isnot necessary to create a new recipe before the inspection operation.

Next, in Step 1154, the inspection operation is carried out inaccordance with the condition and sequence defined in the recipe, andthus the wafer is inspected. The defect extraction is executedimmediately upon each discovery of the defect during the inspectionoperation, and the extracted defect is classified in Step 1155, in whichthe data on the location and others of the extracted defect isaccumulated together with the classification data and the image of thedefect, while the defect information, such as the location of thedefect, on the extracted defect may be displayed on the operating screen(Step 1156). In this way, when the inspection of the wafer is completed,the wafer is ejected (Step 1157), and the next wafer is transferred inposition, on which a series of above steps are repeated. It is to benoted that the path 1158 indicates that if the previously preparedrecipe is used in the inspection, the creation of a new recipe is notnecessary prior to the inspection operation.

In FIG. 24, the inspection operation (Step 1154) executes the inspectionof the wafer in accordance with the condition and sequence described inthe recipe. The defect extraction is executed immediately at each timewhen the defect is found during the inspection operation, and thefollowing operations from a) to c) are performed substantially inparallel.

a) The defect classification (Step 1155) is executed, and the data onthe extracted defect and the data on the defect classification are addedto a file for outputting the result.

b) An image of the extracted defect is added to a file for outputtingthe result exclusively for the image or the file for outputting theresult specified in said a) (Step 1156).

c) The defect data such as the location of the extracted defect isindicated on the operating screen.

Once the inspection has been completed as per each wafer subject to theinspection, then the following operations from a) to c) are performedsubstantially in parallel.

a) The file for outputting the result is closed and saved.

b) When the external communication requests the inspection result, inresponse thereto the inspection result is sent.

c) The wafer is ejected.

In the case where the serial inspection of the wafers is set, the nextwafer to be inspected is transferred and the above operations arerepeated.

The flow in FIG. 24 will be described further in detail.

(1) Making of Recipe (Step 1153)

The recipe is a file for setting a condition or the like involved in theinspection and also can be saved. The recipe is used during or beforethe inspection so as to make a setting for the apparatus, and thecondition on the inspection defined in the recipe includes:

a) The die subject to the inspection;

b) The region subject to the inspection within the die;

c) The inspection algorithm;

d) The condition for detection (conditions required in the defectextraction, including the inspection sensibility and the like); and

e) The condition for observation (conditions required in theobservation, including the magnification, the lens voltage, the stagespeed, the sequence of inspection and so on). The inspection algorithmof c) will be described later more specifically.

Among those items listed above, the setting of the die subject to theinspection may be performed by an operator who designates the die to beinspected on a die map diagram displayed in the operating screen, asshown in FIG. 25. In the example illustrated in FIG. 25, the die “a”located in an edge area of the wafer and the die “b” that has beendetermined to be defective beyond any doubt in the previous step aregrayed out to preclude them from the inspection, and the rest of thedies are subject to the inspection. The apparatus further includes afunction for designating the die subject to inspection automaticallybased on the distance from the edge of the wafer and/or the informationon whether the die is good or bad, which has been detected in theprevious step.

Further, to set the region subject to the inspection within the die, theoperator may designate the region subject to the inspection on a diagramfor setting a region to be inspected within the die displayed in theoperating screen by using an input device, such as a mouse, based on theimage obtained by the optical microscope or the EB microscope. In theexample illustrated in FIG. 26, the region 1161 indicated by the solidline and the region 1162 indicated by the broken line have been set asthe regions subject to the inspection.

The region 1161 includes substantially entire area of the die that hasbeen set as the region subject to the inspection. The inspectionalgorithm specifies the adjacent die comparison method (i.e., thedie-to-die inspection), in which the details of the condition on thedetection and the condition on the observation applied to this regionmay be separately established. As for the region 1162, the inspectionalgorithm specifies the array inspection (i.e., cell-to-cellinspection), in which the details of the condition on the detection andthe condition on the observation applied to this region may beseparately established. This means that it is possible to set aplurality of regions subject to the inspection, and for each of thoseregions subject to the inspection, the individual conditions on theinspection algorithm and/or on the inspection sensibility can be setrespectively. Further, the regions subject to the inspection can beplaced on one another, and in this case, different sets of inspectionalgorithm may be applied to the same region simultaneously.

(2) Inspection Operation (Step 1154)

In the inspection operation, the wafer subject to the inspection isdivided into segments each defined by a certain scanning width as shownin FIG. 27 and scanned. The scanning width is determined substantiallybased on a length of the line sensor, and the line sensor is arrangedsuch that the end portions of the line sensor are slightly overlappedwith each other. This is intended to provide a correct judgment on thecontinuity between lines when the detected defects are to be processedintegrally in a final stage and to ensure an extra margin for the imagealignment when the comparative inspection is carried out. The amount ofoverlapping may be about 16 dots for the 2048 dots of line sensor.

FIG. 28 (A) and FIG. 28(B) schematically show the direction and sequenceof the scanning operation, respectively. The operator may select eitherone of a bi-directional operation A aiming for reducing the inspectiontime or a unidirectional operation B due to the mechanical constraint.Further, the apparatus has a function for automatically calculating anoperation for reducing the scanning amount based on the setting in therecipe for the die subject to the inspection and for carrying out thisoperation. FIG. 29 illustrates an example of scanning operation for acase where there is a single die 1171 subject to the inspection, whereinan unnecessary scanning operation is not performed.

The algorithm to be implemented in the present apparatus may becategorized principally into two types:

1. An array inspection (Cell inspection); and

2. A random inspection (Die inspection),

where the random inspection may be further classified depending on theobject to be compared as follows;

a) An adjacent die comparison method (Die-Die inspection);

b) A reference die comparison method (Die-Any die inspection); and

c) A CAD data comparison method (Cad Data-Any Die inspection).

A method generally referred to as a golden template method includes b)the reference die comparison method and c) the CAD data comparisonmethod, wherein in the reference die comparison method, the referencedie is used as the golden template, and in the CAD data comparisonmethod, the CAD data is used as the golden template. An operation inaccordance with each algorithm will be described below.

(1) Array Inspection (Cell Inspection)

The array inspection may be applied to the inspection of a cyclicstructure. One example thereof may be represented by a DRAM cell. Inthis inspection, an image to be inspected is compared with a referenceimage and a difference therebetween is extracted as a defect. Thereference image and the image subject to the inspection may be eitherone of a two-valued image or a multi-valued image for improving thedetection precision. The difference between the reference image and theimage subject to the inspection may be in itself treated as the detecteddefect, and a secondary determination for avoiding a detection error maybe further performed based on the difference data, including adifferential amount of the detected difference and a total area of thepixels containing the difference.

In the array inspection, the comparison between the reference image andthe image subject to the inspection may be carried out on a structuralcycle basis. That is, the comparison may be performed by everystructural cycle while reading out the images that have been obtained atonce by a CCD, or otherwise if the reference image is defined by nstructural cycles, the comparison may be performed by every n structuralcycle.

One example of a method for generating the reference image is shown inFIG. 30, in which an example for making the comparison by everystructural cycle is illustrated so as to represent single structuralcycle generation. The same method may be employed to make the number ofcycles to n. On the assumption, the direction of the inspection in FIG.30 is indicated by an arrow A. Besides, the cycle indicated by t₄denotes a cycle subject to the inspection. Since the operator can inputa size representing the cycle while watching the screen, therefore thecycles t₁ to t₆ can be easily identified in FIG. 30.

A reference cycle image may be generated by adding the data in thecycles t₁ to t₃ just before the cycle subject to the inspection in eachpixel and averaging the result. Even if a defect is contained in eitherone of the t₁ to t₃ cycle images, they are averaged and consequentlyless affective to the outcome. Thus formed reference cycle image and theimage of the cycle t₄ to be inspected are compared to each other toextract the defect.

In the next step, when the image of the cycle t₅ subject to theinspection is to be inspected, the data in the cycles t₂ to t₄ are addedand averaged to thereby generate the reference cycle image. In thefollowing steps of inspection, the reference cycle image may begenerated successively in a similar manner from the images obtainedbefore the image of the cycle to be inspected having been taken so as tocontinue the inspection operation.

(2) Random Inspection (Die Inspection)

The random inspection may be applied without restriction of thestructure of a die. In the inspection, an image subject to theinspection is compared with a reference image as an image to be referredto and a difference therebetween is extracted as a defect. The referenceimage and the image subject to the inspection may be either one of atwo-valued image or a multi-valued image for improving the detectionprecision. The difference between the reference image and the imagesubject to the inspection may be in itself treated as the detecteddefect, and a secondary determination for avoiding a detection error maybe further performed based on the difference data, including adifferential amount of the detected difference and a total area of thepixels containing the difference.

The random inspection may be classified based on how to determine thereference image. An operation specific to the method for determining thereference image will now be described.

A. An Adjacent Die Comparison Method (Die-Die Inspection)

The reference image is an image of a die adjacent to another die whoseimage is to be inspected. The image of a die subject to the inspectionis compared with two reference images of dies located adjacent to saiddie subject to the inspection to thereby determine a defect. This methodis illustrated in FIGS. 31 and 32, wherein under a condition where aswitch 1185 and a switch 1186 are set such that a memory 1181 and amemory 1182 of an image processor are connected to a path 1184 from acamera 1183, the following steps a) through i) are executed.

a) A step of storing a die image 1 (FIG. 31) from the path 1184 into thememory 1181 in accordance with a scanning direction “S”.

b) A step of storing a die image 2 from the path 1184 into the memory1182.

c) A step of obtaining the die image 2 from the path 1187 insynchronization with said step b), and comparing the thus obtained dieimage 2 with the image data stored in the memory 1181, which representthe data in the same relative position in the die, to thereby determinea difference between them.

d) A step of saving the difference from said step c).

e) A step of storing a die image 3 from the path 1184 into the memory1181.

f) A step of obtaining the die image 3 from the path 1187 insynchronization with said step e), and comparing the thus obtained dieimage 3 with the image data stored in the memory 1182, which representthe data in the same relative position in the die, to thereby determinea difference between them.

g) A step of saving the difference from said step f).

h) A step of determining a defect in the die image 2 from the resultsstored in said steps d) and g).

i) A step of sequentially repeating said steps a) through h) on a seriesof dies.

Depending on the specific setting, prior to the step of determining thedifferences in said c) and f), the compensation may be applied so as tocancel the positional difference between two images to be compared(position alignment). Alternatively, the compensation may be applied soas to cancel the density difference therebetween (density alignment).Otherwise, both of said alignments may be applied.

B. A Reference Die Comparison Method (Die-Any Die Inspection)

The operator designates a reference die. The reference die may be a dieexisting on the wafer or another die whose image has been stored priorto the inspection, and first of all, the reference die is scanned or theimage having stored in advance is transferred so that the image may bestored in a memory as a reference image. Steps a) through h) to becarried out in this method will be described below with reference toFIGS. 31 and 32.

a) A step of selecting by the operator the reference die from the dieson the wafer subject to the inspection or from the die images havingbeen stored prior to the inspection.

b) In the case of the reference die existing on the wafer subject to theinspection, a step of setting the switch 1185 and the switch 1186 suchthat at least either one of the memory 1181 or the memory 1182 of theimage processor is connected to the path 1184 from the camera 1183.

c) In the case of the reference image being represented by the die imagehaving been stored prior to the inspection, a step of setting the switch1185 and the switch 1186 such that at least either one of the memory1181 or the memory 1182 of the image processor is connected to the path1189 from a memory 1188 storing the reference image representing the dieimage.

d) In the case of the reference die existing on the wafer subject to theinspection, a step of scanning the reference die and transferring thereference image representing the reference die image into a memory ofthe image processor.

e) In the case of the reference image being represented by the die imagehaving been stored prior to the inspection, a step of transferring thereference image representing the reference die image into the memory ofthe image processor without any necessity for the step of scanning.

f) A step of comparing the images obtained by scanning the dies subjectto the inspection in sequence with the image in the memory formed by thetransferred reference image which is the reference die image and/or theimage in which the data in the same relative position in the die is thesame, and thereby determining a difference therebetween.

g) A step of determining a defect from the difference obtained in saidstep f).

h) A step of repeating said procedure as defined in the above steps d)through g) by inspecting the scanning position of the reference and theportion on the die to be inspected, which corresponds to the scanningposition on the reference die, across the entire area of the wafercontinuously, as shown in FIG. 34, while changing the scanning positionon the reference die until the die to be inspected is entirelyinspected.

Depending on the specific setting, prior to the step of determining thedifferences in said step f), the compensation may be applied so as tocancel the positional difference between two images to be compared(position alignment). Alternatively, the compensation may be applied soas to cancel the density difference therebetween (density alignment).Otherwise, both of said alignments may be applied.

In said step d) or e), the reference die image stored in the memory ofthe image processor may be an entire image of the reference die or apartial image thereof, and if the partial image of the reference die istaken as the reference die image, then the partial image of thereference die shall be renewed continuously during the inspection.

C. A CAD Data Comparison Method (CadData-AnyDie Inspection)

In the semiconductor manufacturing process shown in FIG. 35, a referenceimage is made from the CAD data representing an output from thesemiconductor pattern designing step by the CAD, as an image to bereferred to. The reference image may an entire image of the die or apartial image thereof containing the area to be inspected.

Since the CAD data is typically represented by the vector data, itcannot be used directly as the data for the reference image, unless itis converted to the raster data corresponding to the image data obtainedby the scanning operation. Accordingly the vector data representing theCAD data should be converted into the raster data, and this conversionmay be executed for each unit defined by the scanning width of the imageobtained by scanning the die subject to the inspection during theinspection. At that time, the conversion may be applied to the imagedata representing the same relative position on the die as of an imageexpected to be obtained by scanning the die subject to the inspection.The inspection scanning and the conversion task may be performed as theyare overlapped.

The above conversion task from the vector data to the raster data may beadded with at least one of the following functions:

a) A function of making the raster data multi-valued;

b) A function of, in conjunction with said a), setting a gradientweighting and/or an offsetting in making the data multi-valued, bytaking the sensibility of the inspection apparatus into account; and

c) A function of, after the vector data is converted into the rasterdata, performing an image processing for processing pixels, includingexpanding and contracting of the pixels.

In FIG. 32, the inspection steps by way of the CAD data comparisonmethod include the following steps a) through f):

a) A step of converting the CAD data into the raster data by acalculator 1190, and making a reference image with said additionalfunction and storing it in the memory 1188;

b) A step of setting the switch 1185 and the switch 1186 such that atleast either one of the memory 1181 or the memory 1182 of the imageprocessor is connected to the path 1184 from the memory 1188;

c) A step of transferring the reference image in the memory 1188 to amemory in the image processor;

d) A step of comparing the images obtained by scanning the dies subjectto the inspection in sequence with the image in the memory formed by thetransferred reference image and/or the image in which the data in thesame relative position in the die is the same, and thereby determining adifference therebetween.

e) A step of determining a defect from the difference obtained in saidstep d); and

f) A step of repeating said procedure as defined in the above steps a)through e) by inspecting the scanning position of the reference die andthe portion on the die to be inspected, corresponds to the scanningposition on the reference die, across the entire area of the wafercontinuously, as shown in FIG. 34, while changing the scanning positionon the reference die until the die to be inspected is entirelyinspected.

Depending on the specific setting, prior to the step of determining thedifferences in said d), the compensation may be applied so as to cancelthe positional difference between two images to be compared (positionalignment). Alternatively, the compensation may be applied so as tocancel the density difference therebetween (density alignment).Otherwise, both of said alignments may be applied.

In said step c), the reference die image stored in the memory of theimage processor may be an entire image of the reference die or a partialimage thereof, and if the partial image of the reference die is taken asthe reference die image, then the partial image of the reference dieshall be renewed continuously during the inspection.

(3) Focus Mapping

FIG. 36 shows a basic flow of the focusing function. Firstly, after awafer transfer (Step 1201) including an alignment operation (Step 1202),a recipe is made, which specifies a condition and the like on involvingthe inspection. One of the recipes is a focus map recipe, and accordingto the focusing information specified in this recipe, an inspectionoperation and a reviewing operation are executed in theautomatic-focusing mode (Step 1204). After this, the wafer is ejected(Step 1205). A procedure for making the focus map recipe along with aprocedure for operating the automatic-focusing will be described below.

1. Procedure for Making the Focus Map Recipe

The focus map recipe has its independent input screen, and the operatorcan make the recipe by executing the following steps a) through c).

a) A step of inputting a focus map coordinate, such as a position of dieand/or a pattern in a die, to which the focus value is to be input bymeans of a position selecting switch 1211 of FIG. 37;

b) A step of setting a die pattern, which is-required in automaticmeasuring of the focus value (it is to be noted that this step may beskipped if the focus value is not measured automatically); and

c) A step of setting a best focus value on the focus map coordinatedetermined in said step a).

It is to be noted that in said step a), the operator can designate anydesired die, and alternatively it is possible to make a setting suchthat the operator may select all of the dies or every n pieces of dies.Further, the operator can select as an input screen a diagramschematically representing an array of dies within the wafer or an imageusing an actual image.

In said step c), the operator can set the best focus value on manual byusing a manual switch 1213 in FIG. 37, or can select and set itautomatically by using a focus switch 1212 operative in association withthe voltage value of a focusing electrode or by using an auto-switch1214.

2. Procedure for Measuring the Focus Value

An exemplary procedure for automatically determining a focus value insaid step c) includes:

a) A step of obtaining an image with the focus position Z=1 andcalculating its contrast, as shown in FIG. 38;

b) A step of performing said step a) with respect to Z=2, 3 and 4,respectively;

c) A step of determining a contrast function through a regression fromthe contrast values obtained in said steps a) and b), and

d) A step of determining by an arithmetic operation the Z that can givea maximum value of the contrast function, and setting this value as thebest focus value.

For example, if such a line and a space as shown in FIG. 39 are chosenas the die pattern necessary for automatically measuring the focusvalue, a good result will be obtained. The contrast is measurable, if itincludes a black and white pattern, regardless of its shape.

By executing the above steps a) through d), the best focus value on onepoint can be determined. A data format at this time is represented by(X, Y, Z), or a set of the coordinate XY used in the determination ofthe focus with the best focus value Z, meaning that the focus mapcoordinate number (X, Y, Z) determined in the focus map recipe isexisting. This is a part of the focus map recipe, and is referred to asa focus map file.

3. Procedure for Operating the Automatic-Focusing

A method for setting the best focus based on the focus map recipe,during the inspection operation for obtaining an image and the reviewingoperation, may be performed in a following manner.

Firstly, the position data is further subdivided based on the focus mapfile 1 made at the time of making the focus map recipe, and the bestfocus at that time is determined by the calculation to thereby make asubdivided focus map file 2. This calculation is executed by using aninterpolation function, which may be specified by the operator duringmaking the focus map recipe, for example, as a linear interpolation, aspline interpolation or the like. Secondly, the XY position of the stageis monitored, and a voltage to be applied to the focusing electrode ischanged to the focus value specified in the focus map file 2.

To explain more specifically, in FIGS. 40(A) through (C), assuming thata black dot indicates the focus value in the focus map file 1 and awhite dot indicates the focus value in the focus map file 2, then thefocus values in the focus map file is used to interpolate the focusvalues in the focus map file, and the Z coordinate of the focusingposition is changed in association with the scanning so as to maintainthe best focusing. At that time, in the space between the specifiedpoints (indicated by the white dots) in the focus map file, a currentvalue is used until the next changing point is encountered.

FIG. 41 shows an example of the manufacturing line using a defectinspection apparatus according to the present invention. It is designedsuch that the information, including a lot number of a wafer subject tothe inspection with the inspection apparatus 1221 and a historyindicating specific manufacturing apparatuses used to manufacture saidwafer, can be read out of the memory arranged in the SMIF or FOUP 1222,or otherwise its lot number can be identified by reading the ID numberof the SMIF, FOUP or the wafer cassette.

The defect inspection apparatus 1221 is adapted to be connected with anetwork system of a production line, and via this network system 1223,it can send the information such as a lot number of a wafer representingan object to be inspected and a result from inspection on the wafer to aproduction line controlling computer 1224 that controls the productionline, respective manufacturing apparatuses 1225, and other inspectionapparatuses. The manufacturing apparatus may include lithography-relatedapparatuses, such as an exposure, a coater, a curing device, and adeveloper, or a film deposition apparatus, such as an etching device, asputtering device and a CVD device, a CMP apparatus, a variety of typesof measuring apparatuses and other inspection apparatuses.

In the inspection of the wafer, it is preferred from the viewpoint ofthe resolution that an image of a surface of the wafer can be obtainedby controlling the electron beam to impinge upon the wafer and detectingthe secondary electrons emanated from the wafer. Based on thisunderstanding, the description has been so far centered mainly to thesecondary electrons, the reflected electrons or the back-scatteredelectrons. However, the electrons to be detected may be any types ofelectrons in so far as the information on the surface of the substratecan be obtained therefrom, including, for example, mirror electrons (ina broad sense, referred to as reflected electrons) that do not directlyimpinge upon the substrate but are reflected in the vicinity of thesubstrate owing to the negative electric field formed in that region, ortransmission electrons that are transmittable through the substrate.Especially, for the case of using the mirror electrons, in which theelectrons do not directly impinge upon the sample, the effect of thecharge-up can advantageously be made extremely low.

For the case of using the mirror electrons, a negative potential lowerthan the accelerating voltage is applied to the wafer, so that thenegative electric field can be formed in the vicinity of the wafer. Thisnegative potential should be favorably set to such a value sufficient tocause almost all of the electrons to be returned in the vicinity of thesurface of the wafer. Specifically, the potential should be set to avalue lower than the accelerating electrons by 0.5 to 1.0V or more. Forexample, in the present invention, for the case of accelerating voltageof −4 kV, preferably, the voltage to be applied to the sample should bein a range of −4.0005 kV to −4.0050 kV. More preferably, it should be ina range of 4.0005 kV to −4.0020 kV, and most preferably in a range of−4.0005 kV to −4.0010 kV.

Further, for the case of using the transmission electrons, when theaccelerating voltage is set at −4 kV, the voltage to be applied to thewafer should be in a range of 0 to −4 kV, preferably in a range of 0 to−3.9 kV, and more preferably in a range of 0 to −3.5 kV. Further, alight ray or an X-ray may be used. These rays are satisfactorilyapplicable to the alignment, the secondary system and the die comparisonin the defect inspection apparatus according to the present invention.

Further, the electrons or the secondary beam to be detected in thedefect inspection apparatus according to the present invention may be ofany types in so far as the information on the sample surface iscontained therein, including, not only the secondary electrons, thereflected electrons (also referred to as the mirror electrons) and theback-scattered electrons, but also those reflected electrons that arereflected in the vicinity of the sample without making the primary beamimpinge upon the sample with the aid of the negative electric fieldformed in the vicinity of the sample. Further, the primary beam is notlimited to the electrons but may be a light ray. In the case of theprimary beam represented by the light ray, the secondary beam is alsothe light ray, and in the case of the UV ray to be used, the secondarybeam may be formed by the electrons.

The defect inspection apparatus according to the present invention,which has been described above, is effectively used, for example, in theinspection step in the semiconductor device manufacturing method asshown in FIGS. 42 and 43. The semiconductor device manufacturing methodwill now be described with reference to FIGS. 42 and 43.

The manufacturing method shown in FIG. 42 includes the following mainprocesses, each of main processes consisting of several sub-processes.

(1) A process P11 for manufacturing a wafer P12 (or preparing a sample).

(2) A mask manufacturing process P21 for fabricating a mask (reticle)P22 to be used in the exposure (or a mask preparing process forpreparing a mask).

(3) A wafer processing process P13 for applying any necessary processingtreatments to the wafer P12.

(4) A chip assembling process P14 for cutting out those chips P15 formedon the wafer P12 one by one to make them operative.

(5) A chip inspection process P16 for inspecting the chips P15 assembledin the chip assembling process P14 and then taking those chips that havesuccessfully passed the inspection as finished products P17.

Among those main processes, one main process that has a critical effecton the performance of the semiconductor device is the wafer processingprocess P13. In this wafer processing process, the designed circuitpatterns are deposited on the wafer one on another, thus to form manychips, which will function as memories or MPUs. This wafer processingprocess P13 includes the following sub-processes.

(A) A thin film deposition process for forming a dielectric thin film tobe used as an insulation layer, a metallic thin film to be formed into awiring section or an electrode section, and the like (by using the CVDprocess or the sputtering);

(B) An oxidizing process for oxidizing thus formed thin film and/or thewafer substrate;

(C) A lithography process P23 for forming a resist pattern by using amask (reticle) P22 in order to selectively process the thin film layerand/or the wafer substrate;

(D) An ions/impurities implant and diffusion process;

(E) A resist stripping process; and

(F) An inspection process for inspecting the processed wafer.

It should be noted that the wafer processing process P13 must be carriedout repeatedly as desired depending on the number of layers contained inthe wafer, thus to manufacture the products (the semiconductor device)P17 that will be able to operate as designed.

The process defining a core process in the wafer processing process P13of FIG. 42 is the lithography process P23, and FIG. 43 shows the stepsperformed in the lithography process P23. The lithography process P23includes:

(a) A resist coating process P31 for coating the resist on the waferhaving a circuit pattern formed thereon in the preceding stage;

(b) An exposing process P32 for exposing the resist;

(c) A developing process P33 for developing the exposed resist to obtainthe pattern of the resist; and

(d) An annealing process P34 for stabilizing the developed resistpattern.

Known procedures may be applied to all of the processes described aboveincluding semiconductor device manufacturing process, the waferprocessing process P13 and the lithography process P23, and any furtherexplanation about those will be omitted.

When a defect inspection apparatus according to the present invention isused in the chip inspection process P16 to perform a defect inspection,even such a semiconductor device having a fine pattern can be inspectedwith high throughput, so that not only a 100% inspection can beemployed, but also it is possible to improve the yield of the productsand to prevent any defective products from being delivered.

INDUSTRIAL APPLICABILITY

As understood from the detailed description on some specific embodimentsof the present invention as given above, the present invention can bringabout following excellent effects:

(1) Since an image is generated while applying a position compensationso that each die may be positioned along an equally spaced grid, theimage can be generated appropriately so as to perform a patterninspection without any problem arising even when a stage carrying asample is not moved as designed or when each die is not formed preciselyin its position specified in design, wherein taking as an example thecase of using an electron beam for scanning to obtain the image, sincewhen being irradiated upon the sample, the electron beam is controlledby a deflector to direct to its appropriate position in order tocompensate for the misalignment of the pattern and also the electronsfrom the sample (i.e., secondary electrons, reflected electrons,back-scattered electrons and transmission electrons) are also controlledby the deflector to apply necessary compensation, therefore the imagefor a desired region can be formed accurately and the generated imagecan be positioned in accordance with an equally spaced virtual grid,thus improving the precision in a defect inspection;

(2) Since, before performing a registration and/or an image-taking, afocusing condition is appropriately measured over an entire region to beinspected and a two-dimensional image is obtained while changing anexcitation voltage of an objective lens in conformity with said focusingcondition, therefore even with the uneven sample surface, the imagehaving a high resolution can be obtained, which is advantageous in thedefect inspection of the sample, such as a stencil mask and a sample;and

(3) Since a semiconductor device can be manufactured while performing adefect inspection in the course of processing or after the completion ofthe processing, a high yield can be expected in the semiconductor devicemanufacturing process.

The present invention has been described in detail by the abovedescription with reference to the attached drawings, which are made forto allow better understanding but not intended to limit the features ofthe present invention. These are made simply to illustrate and explainthe preferred embodiments of the present invention, and it should beunderstood that all of the variations and modifications to be madewithout departing from the scope of the spirit of the present inventionshall be protected. The entire disclosure of Japanese Patent ApplicationNos. 2003-290021 filed on Aug. 8, 2003; 2003-161589 filed on Jun. 6,2003; 2003-153902 filed on May 30, 2003; 2004-046868 filed on Feb. 23,2004; and 2004-056134 filed on Mar. 1, 2004, each includingspecification, claims drawings and summary is incorporated herein byreference in its entirety.

1. A method for inspecting patterns within a plurality of dies locatedapproximately regularly along two axial directions that are not parallelwith respect to each other on a substrate, said method comprising stepsof: (a) generating a target grid according to which said dies on saidsubstrate should be virtually placed; (b) determining an actual positioncoordinate of each die on said substrate; (c) calculating a positionerror of said each die with respect to said target grid and; (d)compensating for the position of the image of said each die to beobtained, based on a value of the position error of said each die andthus obtaining the image; and (e) performing an inspection of thepattern to detect defects within the pattern of said die based on theimage obtained after said position thereof is compensated for, whereinin said step (a), said target grid is generated in such a manner that atleast two dies are selected in each of two axial directions from aplurality of dies formed across a surface of said substrate along thetwo axial directions that are not parallel to each other, and from apitch between selected dies, a virtual pitch per die is determined alongeach of said two directions, and then based on said virtual pitch, saidtarget grid is generated, and wherein in said step (a), said two dies onsaid sample are selected to thereby detect a pitch between said dies,which is determined as a first pitch; said first pitch is multiplied bya predetermined multiplier, and the thus obtained value is determined asa second pitch; an actual pitch between two dies that are spaced by adistance proximal to said second pitch is detected, which is determinedas a third pitch; and a value determined by dividing said third pitch bysaid multiplier is taken as said virtual pitch, displaying and/orstoring the defects detected.
 2. A method for inspecting patterns withina plurality of dies located approximately regularly along two axialdirections that are not parallel with respect to each other on asubstrate, said method comprising steps of: (a) generating a target gridaccording to which said dies on said substrate should be virtuallyplaced; (b) determining an actual position coordinate of each die onsaid substrate; (c) calculating a position error of said each die withrespect to said target grid and; (d) compensating for the position ofthe image of said each die to be obtained, based on a value of theposition error of said each die and thus obtaining the image; and (e)performing an inspection of the pattern to detect defects within thepattern of said die based on the image obtained after said positionthereof is compensated for, wherein said two axes that are not parallelwith respect to each other represent the X-axis and the Y-axis that areorthogonal to each other, and wherein in said step (a), the virtualpitch between dies is determined by using a dicing line parallel to theX-axis or the Y-axis or a predetermined pattern within said diesdisplaying and/or storing the defects detected.
 3. A method forinspecting a surface of a sample, comprising steps of: irradiating abeam toward said surface of the sample and measuring a size of saidsurface of the sample per pixel within the beam irradiated region;calculating a travel distance of a stage by using said size andperforming an aligning operation of said sample based on a result fromsaid calculation; and irradiating the beam onto said sample anddetecting a secondary beam that has been emanated from said surface ofthe sample by the irradiation of the beam and contains the informationof said surface of the sample, and thereby inspecting defects of saidsurface of the sample, displaying and/or storing the defects detected.4. A method in accordance with claim 3, in which said step of measuringthe size is carried out by measuring a number of pixels of a patternhaving a known size.
 5. A method in accordance with claim 3, in whichsaid step of inspecting said surface of the sample includes a step ofobtaining an image of said region subject to the inspection containing aplurality of pixels by using a CCD or a CCD-TDI and then inspecting saidsurface of the sample by comparing the thus obtained image with areference image.
 6. A method in accordance with claim 5, in which saidstep of inspecting said surface of the sample is carried out, for anarea including patterns within a die defining a cyclic structure, bymeans of the comparison among said cyclic structures within the samedie, but for an area including patterns not defining a cyclic structureby means of the comparison with said reference image.
 7. A method forevaluating a sample surface with an electron beam incident to the samplesurface having a plurality of pixels, said method comprising steps of:(a) irradiating an electron beam onto a sample and detecting secondaryelectrons or back-scattered electrons; (b) amplifying and A/D convertinga detected signal to thereby form a two-dimensional image containing adensity data and inputting said formed image on a predetermined firstregion into a memory; (c) forming a two-dimensional image having adensity data on a second region expected to contain the same pattern asof the region whose image has been input in said step (b) and inputtingthe formed image into another memory; (d) performing a density matchingbetween the image obtained in said step (b) and the image obtained insaid step (c) and then increasing or decreasing the density of one ofsaid two images so as to match the average density between said twoimages; (e) performing a pattern matching between the images having theaverage density matched to each other, calculating a difference betweenimages to which the pattern matching has been applied, and then takingthe location having the difference as a candidate for a defect; and (f)obtaining a two-dimensional image of a third region expected to containthe same pattern as said first and said second regions, performing adensity matching of said two-dimensional image in said third region withthe image of said first or said second region, comparing to thecandidate for the defect obtained in said step (e), and determining thedefect from said candidate for the defect, wherein said electron beam isa multi-beam which consists of a plurality of beams arranged such thatwhen said plurality of beams is projected in one axial direction, eachbeam is equally spaced from adjacent beam, and is adapted to make ascanning operation in a direction orthogonal to said one axialdirection, wherein said two-dimensional image is formed by electricallycontrolling said multi-beam so as to make the scanning operation whilemoving a sample table continuously in the direction parallel to said oneaxial direction, displaying and/or storing the defects detected.
 8. Amethod for evaluating a sample surface with an electron beam incident tothe sample surface having a plurality of pixels, said method comprisingsteps of: (a) irradiating an electron beam onto a sample and detectingsecondary electrons or back-scattered electrons; (b) amplifying and A/Dconverting a detected signal to thereby form a two-dimensional imagecontaining a density data and inputting said formed image on apredetermined first region into a memory; (c) forming a two-dimensionalimage having a density data on a second region expected to contain thesame pattern as of the region whose image has been input in said step(b) and inputting the formed image into another memory; (d) performing adensity matching between the image obtained in said step (b) and theimage obtained in said step (c) and then increasing or decreasing thedensity of one of said two images so as to match the average densitybetween said two images; (e) performing a pattern matching between theimages having the average density matched to each other, calculating adifference between images to which the pattern matching has beenapplied, and then taking the location having the difference as acandidate for a defect; and (f) obtaining a two-dimensional image of athird region expected to contain the same pattern as said first and saidsecond regions, performing a density matching of said two-dimensionalimage in said third region with the image of said first or said secondregion, comparing to the candidate for the defect obtained in said step(e), and determining the defect from said candidate for the defect,wherein in said step (d), said density matching is carried out such thatfirstly offset values are matched so as for the lowest densities of saidtwo images to match to each other and then a gain is adjusted so as forthe highest densities of said two images to match to each other,displaying and/or storing the defects detected.